<figure><img src="image_1.png" /></figure>

# The Next Generation Virgo Cluster Survey (NGVS). XIV. The Discovery of Low-mass Galaxies and a New Galaxy Catalog in the Core of the Virgo Cluster*

Laura Ferrarese<fnref n="1" />, Patrick Côté<fnref n="1" />, Lauren A. MacArthur<fnref n="1" />,<fnref n="2" />, Patrick R. Durrell<fnref n="3" />, S. D. J. Gwyn<fnref n="1" />, Pierre-Alain Duc<fnref n="4" />,<fnref n="5" />,
Rúben Sánchez-Janssen<fnref n="1" />,<fnref n="6" />, Matthew Santos<fnref n="1" />,<fnref n="7" />, John P. Blakeslee<fnref n="1" />,<fnref n="8" />, Alessandro Boselli<fnref n="9" />, Fred Boyer<fnref n="3" />, Michele Cantiello<fnref n="10" />,<fnref n="11" />,
Stéphane Courteau<fnref n="11" />, Jean-Charles Cuillandre<fnref n="4" />, Eric Emsellem<fnref n="12" />, Thomas Erben<fnref n="13" />, Giuseppe Gavazzi<fnref n="14" />,
Puragra Guhathakurta<fnref n="15" />, Marc Huertas-Company<fnref n="16" />,<fnref n="17" />, Andrés Jordán<fnref n="18" />,<fnref n="19" />, Ariane Lançon<fnref n="5" />, Chengze Liu<fnref n="20" />,
Simona Mei<fnref n="16" />,<fnref n="17" />, J. Christopher Mihos²¹, Eric W. Peng<fnref n="22" />,<fnref n="23" />, Thomas H. Puzia<fnref n="18" />, Joel Roediger<fnref n="1" />, David Schade<fnref n="1" />,
James E. Taylor<fnref n="7" />, Elisa Toloba<fnref n="15" />,<fnref n="24" />, and Hongxin Zhang<fnref n="18" />,<fnref n="22" />,<fnref n="25" />,<fnref n="26" />

Received 2016 January 20; revised 2016 July 5; accepted 2017 February 2; published 2020 February 19

## Abstract

The Next Generation Virgo Cluster Survey (NGVS) was designed to provide a deep census of baryonic structures in the Virgo cluster. The survey covers the 104 deg<fnref n="2" /> area from the core of Virgo out to one virial radius, in the u*griz bandpasses, to a point-source depth of g ~ 25.9 mag (10σ) and a single pixel surface brightness limit of µg ~ 29 mag arcsec⁻<fnref n="2" /> (2σ above the sky). Here we present the final catalog of 404 Virgo galaxies located within a 3.71 deg<fnref n="2" /> (0.3 Mpc<fnref n="2" />) region centered on M87, Virgo's dominant galaxy. Of these, 154 were previously uncataloged and span the range 17.8 mag < g < 23.7 mag (−13.4 mag < Mg < −7.4 mag at the 16.5 Mpc distance of Virgo). Extensive simulations show that the NGVS catalog is complete down to g = 18.6 mag (Mg = −12.5 mag, corresponding to a stellar mass M ~ 1.6 × 10⁷ M☉ for an old stellar population), and 50% complete at g = 22.0 mag (Mg = −9.1 mag, M ~ 6.2 × 10⁵ M☉). The NGVS 50% completeness limit is 3 mag deeper than that of the Virgo Cluster Catalog (VCC), which has served as Virgo's reference standard for over a quarter century, and 2 mag deeper than the VCC detection limit. We discuss the procedure adopted for the identification of objects and the criteria used to assess cluster membership. For each of the 404 galaxies in the NGVS Virgo Cluster core catalog, we present photometric and structural parameters based on a nonparametric curve-of-growth and isophotal analysis, as well as parametric (Sérsic, double-Sérsic, and/or core-Sérsic) fits to the one-dimensional surface brightness profiles and two-dimensional light distributions.

**Key words:** galaxies: clusters: individual (Virgo) – galaxies: distances and redshifts – galaxies: fundamental parameters – galaxies: nuclei – galaxies: stellar content – galaxies: structure

**Supporting material:** machine-readable tables

<footnote n="1">¹ National Research Council of Canada, Herzberg Astronomy and Astrophysics Research Centre, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada</footnote>

<footnote n="2">² Princeton University, Department of Astrophysical Sciences, Princeton, NJ 08544, USA</footnote>

<footnote n="3">³ Department of Physics and Astronomy, Youngstown State University, Youngstown, OH 44555, USA</footnote>

<footnote n="4">⁴ CEA/IRFU/SAP, Laboratoire AIM Paris-Saclay, CNRS/INSU, Université Paris Diderot, Observatoire de Paris, PSL Research University, F-91191 Gif-sur-Yvette Cedex, France</footnote>

<footnote n="5">⁵ Observatoire Astronomique, Université de Strasbourg & CNRS UMR 7550, 11 rue de l'Université, F-67000 Strasbourg, France</footnote>

<footnote n="6">⁶ 1 Royal Observatory Edinburgh, UK Astronomy Technology Centre, Blackford Hill, Edinburgh EH9 3HJ, UK</footnote>

<footnote n="7">⁷ Department of Physics and Astronomy, University of Waterloo, Waterloo, ON N2L 3G1, Canada</footnote>

<footnote n="8">⁸Gemini Observatory, South Operations Center, c/o AURA, Casilla 603 La Serena, Chile</footnote>

<footnote n="9">⁹ Aix Marseille Université, CNRS, Laboratoire d'Astrophysique de Marseille, UMR 7326, F-13388 Marseille, France</footnote>

<footnote n="10">¹⁰ INAF, Osservatorio Astronomico di Teramo, I-64100 Teramo, Italy</footnote>

<footnote n="11">¹¹ Department of Physics, Engineering Physics and Astronomy, Queen's University, Kingston, ON, Canada</footnote>

<footnote n="12">¹²European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748, Garching, Germany</footnote>

<footnote n="13">¹³ Argelander-Institut für Astronomie, University of Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany</footnote>

<footnote n="14">¹⁴ Universita degli Studi di Milano-Bicocca, Piazza della Scienza 3, I-20126 Milano, Italy</footnote>

<footnote n="15">¹⁵ UCO/Lick Observatory, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA</footnote>

<footnote n="16">¹⁶ GEPI, Observatoire de Paris, PSL Research University, CNRS, University of Paris Diderot, 61, Avenue de l'Observatoire, F-75014, Paris, France</footnote>

<footnote n="17">¹⁷ University of Paris Denis Diderot, University of Paris Sorbonne Cité (PSC) F-75205, Paris Cedex 13, France</footnote>

<footnote n="18">¹⁸ Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, 7820436 Macul, Santiago, Chile</footnote>

<footnote n="19">¹⁹ Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Av Diagonal las Torres 2640, Peñalolén, Santiago, Chile</footnote>

<footnote n="20">²⁰ Center for Astronomy and Astrophysics, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China
²¹ Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106, USA</footnote>

<footnote n="22">²² Department of Astronomy, Peking University, Beijing 100871, People's Republic of China</footnote>

<footnote n="23">²³ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People's Republic of China</footnote>

<footnote n="24">²⁴ Department of Physics, Texas Tech University, Box 41051, Lubbock, TX 79409, USA</footnote>

<footnote n="25">²⁵ CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China</footnote>

<footnote n="26">²⁶ School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, People's Republic of China</footnote>

<footnote>* Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii.</footnote>
# 1. Introduction

At a distance of 16.5 Mpc (Mei et al. 2007; Blakeslee et al. 2009), the Virgo cluster is the center of the Local Supercluster and the dominant mass concentration within 50 Mpc. With thousands of member galaxies lying at nearly a common distance and spanning virtually all known morphological types, Virgo has historically played a key role in studies of how galaxies form and evolve in dense environments. In particular, its core has long been recognized as an extreme environment that offers a unique, and invaluable, observational window into a large range of astrophysical phenomena. Permeated by diffuse intracluster light and an extensive web of filaments (Mihos et al. 2005), the 4 deg² region (~0.33 Mpc²) immediately surrounding M87—the giant elliptical and powerful active galactic nucleus at the bottom of Virgo’s gravitational potential well—is home to ~15,000 globular clusters (Durrell et al. 2014, by far the richest globular cluster system in the local universe), over 100 Ultra Compact Dwarfs (UCDs, Liu et al. 2015), and close to 300 galaxies, that is, almost 15% of the known galaxy population in the entire cluster, while encompassing less than 4% of its area.

To this day, the catalog that still stands as the standard reference for the galaxy population in Virgo is the Virgo Cluster Catalog (VCC) of Binggeli et al. (1985). Beginning in the late 1970s, the authors capitalized on the wide-field imaging capabilities of the 2.5 m du Pont telescope at Las Campanas Observatory to carry out photographic imaging of Virgo down to an extended-source completeness limit of $B \sim 18$ mag ($M_B \sim -13$). Their resultant catalog identified and classified 1851 certain (“M”) or possible (“P”) cluster members<fnref n="27" /> over an area of ~140 deg². Since then, Virgo, and its core in particular, has been the target of several studies specifically designed to extend its galaxy luminosity function beyond the limit probed by the VCC.<fnref n="28" /> The first such study was published by Impey et al. (1988), who covered an area of ~5 deg² using UK Schmidt plates, adding 27 galaxies with “unusually low surface brightness and large angular size” to the existing VCC sample.<fnref n="29" />

After a 15 yr lull,<fnref n="30" /> the galaxy population in the cluster was again targeted in three independent studies by Trentham & Tully (2002), Trentham & Hodgkin (2002), and Sabatini et al. (2003). Trentham & Tully (2002) surveyed a ~0.76 deg² region with Suprime-Cam on Subaru and reported 43 galaxies

not included in the VCC. Trentham & Hodgkin (2002) covered a 24.9 deg² region with the Isaac Newton Telescope (INT) Wide Field Camera, using a B-band filter, reporting 142 new detections. The same telescope/camera combination was used by Sabatini et al. (2003) to cover two strips, the first extending east from the cluster center and the second extending north, for a total coverage of 25 deg². A catalog of sources detected in the 14 deg² east-west strip, including 171 objects not cataloged in the VCC, was presented in Sabatini et al. (2005). Finally, after another 10 yr hiatus, an area of 3.75 deg² was surveyed by Lieder et al. (2012) in the V- and I-bands with the CFH12K camera at the Canada-France-Hawaii Telescope (CFHT). The authors detected 77 galaxies not cataloged in the VCC.

None of the above studies required spectroscopic confirmation of membership, which was instead assessed based on morphology and surface brightness. Although the exact implementation differs among the various studies, the basic idea is that at any given apparent magnitude, Virgo galaxies have lower surface brightness than background sources. Furthermore, morphologically, Virgo members are either smooth or, in the case of late-type dwarfs, have an irregular structure: a grand design spiral structure or a clear bulge/disk morphology is generally indicative of a more distant and more massive system. Binggeli et al. (1985) and Lieder et al. (2012) detect and classify cluster members based on visual inspection of the images. Trentham & Hodgkin (2002) and Trentham & Tully (2002) adopted an automated algorithm for the detection and then made use of inner and outer concentration parameters (derived from aperture photometry) to roughly separate Virgo members from background sources. They do stress, however, that a follow-up detailed visual inspection is crucial for a final classification. Sabatini et al. (2003) were the first to adopt a fully automated detection/membership algorithm. They were also the first (among the aforementioned studies) to apply image-enhancement techniques. Their procedure relies on image convolution to improve the signal-to-noise ratio (S/N) of low surface brightness objects, using an exponential filter with varying scale size designed to match the objects of interests. The selection of Virgo members was further aided by a set of simulations probing the range in surface brightness and scale length over which the ratio of Virgo members to background galaxies is maximized.

The depth of the above surveys varies, but the limit to which the authors claim to be complete is $M_B \sim -11$ to $-10.5$ mag. The ~2 mag improvement over the VCC, however, comes at the expense of a much reduced spatial coverage, a factor of ~6 to ~180 below what was covered by Binggeli and collaborators. This paper presents a new galaxy catalog in the Virgo core based on data from the Next Generation Virgo Cluster Survey (NGVS, Ferrarese et al. 2012, hereafter NGVS-I) a comprehensive optical imaging survey of the Virgo cluster using the 1 deg² MegaCam instrument on CFHT. The NGVS surveyed the Virgo cluster out to the virial radius of its two main substructures—for a total areal coverage of 104 deg²—in the $u^*, g, i, z$ passbands, with partial coverage in $r$. Thanks to a dedicated data-acquisition strategy and processing pipeline, the NGVS reaches a 10σ point-source depth of $g \sim 25.9$ mag and a surface brightness limit of $\mu_g \sim 29$ mag arcsec⁻² (2σ above the mean sky level) at subarcsecond spatial resolutions. Galaxies as faint as $M_g \sim -7.4$ mag have been discovered in the NGVS data, which, as we show in this paper, have a 50% completeness limit of $M_g = -9.13$ mag for extended sources.

<footnote n="27">²⁷ In a subsequent work (Binggeli et al. 1993), the number of certain or possible members was revised to 1815 based on new and improved velocity information.</footnote>

<footnote n="28">²⁸ A different approach was followed by Kim et al. (2014). Their Extended Virgo Cluster Catalog (EVCC) aimed at extending the spatial coverage of the VCC, rather than its depth, and was based on spectra from the Sloan Digital Sky Survey (SDSS) DR7 release, covering an area of 725 deg². Of their spectroscopically confirmed ($v < 3000$ km s⁻¹) 1589 Virgo members, 676 are not cataloged in the VCC.</footnote>

<footnote n="29">²⁹ It is worth pointing out that the VCC did include several (~20) examples of “very-large-size, low-surface-brightness dwarfs” (Binggeli et al. 1985), to which Sandage & Binggeli (1984) refer as “a new type of very large diameter (10,000 pc), low central surface brightness ($\gtrsim 25$ B mag arcsec⁻²) galaxy, that comes in both early (i.e., dE) and late (i.e., Im V) types.” These objects are analogous to the class of Ultra Diffuse Galaxies (UDGs) recently rediscovered in the Virgo and Coma clusters (van Dokkum et al. 2015; Koda et al. 2015).</footnote>

<footnote n="30">³⁰ In 1998, Young and Currie published a catalog of 1180 galaxies within a 23 deg² area in the direction of Virgo. The completeness limit of their survey, conducted on photographic plates at the 1.2 m UK Schmidt Telescope, is similar to that of the VCC, although benefiting from photometry in three filters ($U, B_J, R_C$) and a primarily automated algorithm for galaxy detections. The authors, however, do not attempt to assign membership, relying rather on the membership from the VCC.</footnote>
In this paper we discuss in detail the methodology used for galaxy detection,<fnref n="31" /> as well as the criteria adopted to assess Virgo membership. We then present a final catalog of 404 Virgo members in a 3.71 deg² (0.3 Mpc²) region roughly centered on M87 (hereafter, the “core region”). Of these, 154 are new detections, while 172 and 78, respectively, have already been cataloged in the VCC or any of the surveys discussed earlier. Within the NGVS series, six publications are based directly on the catalog presented here: an estimation of the stellar-to-halo mass ratio and galaxy formation efficiency for galaxies in the core of Virgo (Grossauer et al. 2015); an investigation of the intrinsic shapes of low-mass galaxies (Sánchez-Janssen et al. 2016); the study of the galaxy luminosity and stellar mass function (Ferrarese et al. 2016); an investigation of structural parameters and galaxy scaling relations (including morphological classification; P. Côté et al. 2019, in preparation); the galaxy color–magnitude relation (Roediger et al. 2017); and a study of the nucleation fraction as a function of galaxy luminosity (Sanchez-Janssen et al. 2019).

This paper is organized as follows: Section 2 briefly describes the data and data reduction. Section 3 presents *VCands*, a new automated algorithm developed to identify and characterize potential Virgo members, with special emphasis on low-mass, low surface brightness galaxies. For the Virgo core region, a visually identified set of bona fide Virgo members was used as a training set, as described in Section 3.1. The initial identification and catalog culling is discussed in Section 3.2, while the criteria used to assess Virgo membership are discussed in Section 3.3. Visual checks of all potential candidates and validation of the final catalog of 404 galaxies is presented in Section 3.4. Section 4 presents an extensive set of simulations aimed at assessing the effectiveness of our method and the completeness of our Virgo catalog, as well as quantifying potential biases in the measured photometric and structural parameters. Both nonparametric and parametric estimations of photometric and structural parameters are presented in Section 5, based on a curve-of-growth analysis, parametric fits to the one-dimensional surface brightness profile (both derived from a full isophotal analysis, Section 5.1), and two-dimensional parametric fits to the light distribution (Section 5.2). A comparison of structural parameters based on the different methods is given in Section 5.3. Conclusions are summarized in Section 6. Finally, the two appendices present a cross correlation of the NGVS catalog with previously published catalogs, as well as a critical discussion of the results recently presented in Davies et al. (2016), based on NGVS data.

Throughout this paper, we assume a distance modulus to the Virgo cluster of 31.09 mag (corresponding to a distance of 16.5 Mpc, Mei et al. 2007; Blakeslee et al. 2009), and we consider as spectroscopic members all galaxies with systemic velocity $v < 3500 \text{ km s}^{-1}$, a cut that includes all objects belonging to the different cluster substructures and their surrounding regions (e.g., Binggeli et al. 1993; Boselli et al. 2014).

All catalogs presented in this paper can be downloaded and queried from the NGVS website: http://astrowww.phys.uvic.ca/~lff/NGVS/.

## 2. Description of the Data

A detailed description of the NGVS—including field placement, observing strategy, data-reduction pipeline, data quality and depth, as well as an exposition of the survey’s science goals and a discussion of imaging and spectroscopic follow-up programs—was provided in NGVS-I. Briefly, the survey covers a slightly elongated region (NGVS-I, Figure 1) defined by the area enclosed within two partially overlapping circles, corresponding to the virial regions of Virgo’s two main subclusters (McLaughlin 1999; Ferrarese et al. 2012). To the north, Virgo’s A subcluster is defined by the larger of the two circles, with radius 5.383 (1.55 Mpc assuming a distance to the Virgo cluster of 16.5 Mpc) and centered on M87. To the south, Virgo’s B subcluster is defined by a smaller circle of radius 3.334 (0.96 Mpc) centered on M49. The entire region subtends an area of 104 deg² and was tiled with 117 MegaCam pointings overlapping by 3', each imaging (after stacking multiple dithered exposures) an area of 1° × 1°.

Each field was observed in four MegaCam filters—$u^*$, $g$, $i$, $z$—whose bandpasses, with the exception of $u^*$, closely (but not exactly) resemble those of their SDSS counterparts (see NGVS-I, Figure 6);<fnref n="32" /> while the original survey strategy called for coverage in the *r*-band as well, *r*-band exposures were only obtained for the core of the cluster (i.e., the region for which a galaxy catalog is presented in the paper) and a few additional fields, due to time lost to weather and mechanical problems. Two separate images were obtained for each field, a *long* exposure, reaching a $10\sigma$ point-source limit of 25.9 mag in the *g*-band, and a *short* exposure designed to recover the centers of galaxies that saturate in the *long* exposures (NGVS-I, Table 2). For all *long* exposures, the observing strategy followed a “step-dither” pattern (see NGVS-I, Section 3.5), whereby the dithered exposures that would normally be acquired in a continuous sequence for each individual field (in each filter) are applied instead to a block of (not necessarily contiguous) fields. This observing strategy (somewhat akin to what is normally adopted for near-infrared observations, see also Erben et al. 2005) allowed the application of the Elixir-LSB reduction package (see NGVS-I Section 4.2). Elixir-LSB produces an accurate map of the spatially varying component of the sky and scattered light background by median averaging all (independent) fields observed in a continuous sequence (in a given filter); this map is then subtracted from each individual exposure within the sequence, before stacking. Typical residuals in the Elixir-LSB-processed, scattered light-subtracted images are 0.2% of the sky background in all filters, corresponding to a surface brightness of ~29 mag arcsec⁻². As discussed at length in Duc et al. (2015), some background variations are still visible after the Elixir-LSB processing. The intrachip regions (13" wide between columns and 80" wide between rows) are recovered by the dithering strategy but do not reach the full exposure time and therefore have lower S/N. Bright, saturated foreground stars are surrounded by faint (surface brightness ≲26.5 mag arcsec⁻² in the *g*-band) extended stellar haloes. Finally, scattered light from Galactic cirrus also affects the images at *g*-band surface brightnesses ≲27 mag arcsec⁻². We do not correct for any of these effects, and indeed our

<footnote n="31">³¹ We stress that this papers focuses on the identification of galaxies, and in particular low-mass galaxies, belonging to the Virgo cluster. The detection of globular clusters and UCDs follows a different methodology that will be discussed elsewhere.</footnote>

<footnote n="32">³² The *i*-band filter used for the NGVS was installed on MegaCam in October 2007 and is sometimes referred to as *i2*. In late 2014, after the completion of the NGVS, all MegaCam filters were replaced; the new filters’ passbands are slightly different from those used for our survey.</footnote>
<figure><img src="image_2.png" /><figcaption>**Figure 1.** A gray-scale, g-band mosaic of the Virgo core region, obtained by joining fields NGVS+0+0, NGVS+1+0, NGVS-1+0, and NGVS-1+1 using Swarp (Bertin et al. 2002). North is up, and east is to the left. Spectroscopically confirmed Virgo galaxies (all belonging to the VCC) are shown in red. Galaxies classified as a certain or probable member in the VCC, but without a systemic velocity measurement, are shown in blue. VCC galaxies brighter than $g = 13$ mag ($M_g < -18.17$ after correcting for the average Galactic extinction in the direction of Virgo) are labeled. Non-VCC galaxies identified by Trentham & Hodgkin (2002), Trentham & Tully (2002), Lieder et al. (2012), Sabatini et al. (2003), Kim et al. (2014), or Mihos et al. (2015) are shown by the green ellipses if they are deemed to be Virgo members based on the NGVS analysis and magenta squares if they are believed to be background objects or spurious detections. For the galaxies deemed to belong to the cluster based on the NGVS analysis, the ellipticity and position angle of the ellipse correspond to the values measured from the NGVS images and averaged between 1" and one effective radius, while the semimajor axis of the ellipse is equal to 10 times the measured effective radius (note that some galaxies display strong isophotal twists and ellipticity changes that are not visible in the images, and therefore in some cases the ellipse is not a good representation of the ellipticity and/or position angle of the galaxy on scales larger than one effective radius).</figcaption></figure>

simulations (Section 4) show that about 10% of artificial galaxies injected in the frames are not recovered by our automated detection algorithm precisely because they fall in a region of variable background (high surface brightness or low S/N). However, we will show (Section 3.4) that these objects are recovered based on visual inspection, and therefore the detection limit for low-mass galaxies is set by noise, rather than residual background variations.

The core region presented in this paper comprises the four separate fields listed in Table 1.33 For the purpose of this work its boundaries are defined as

$$12^{\text{h}}26^{\text{m}}20^{\text{s}} \le \alpha(\text{J2000}) \le 12^{\text{h}}34^{\text{m}}10^{\text{s}}, \\ 11^{\circ}30'22'' \le \delta(\text{J2000}) \le 13^{\circ}26'45''.$$

The actual images extend slightly beyond these boundaries (by about 1' in each direction); however, the very edges of the fields are not as well sampled by the dithering pattern and

<table><caption>**Table 1**
Virgo Core Region Field Coordinates</caption><thead><tr><th>Field<br>(1)</th><th>R.A. (J2000)<br>(2)</th><th>Decl. (J2000)<br>(3)</th></tr></thead><tbody><tr><td>NGVS+0+0</td><td>12<sup>h</sup>32<sup>m</sup>11<sup>s</sup></td><td>12<sup>°</sup>00′37″</td></tr><tr><td>NGVS+0+1</td><td>12<sup>h</sup>32<sup>m</sup>11<sup>s</sup></td><td>12<sup>°</sup>56′37″</td></tr><tr><td>NGVS-1+0</td><td>12<sup>h</sup>28<sup>m</sup>18<sup>s</sup></td><td>12<sup>°</sup>00′26″</td></tr><tr><td>NGVS-1+1</td><td>12<sup>h</sup>28<sup>m</sup>17<sup>s</sup></td><td>12<sup>°</sup>56′37″</td></tr></tbody></table>

**Note.** The field name (column 1) indicates the approximate number of degrees of separation, in R.A. and decl., from the field containing M87 (NGVS+0+0). The R.A. and decl. of the center of each field are given in columns 2 and 3.

therefore have lower S/N. They have been excluded from the analysis presented in this paper but are recovered in neighboring fields, and the galaxies within will be included in the full cluster catalog. A mosaic of the core region is shown in Figure 1: M87 (VCC 1316) is the most luminous galaxy slightly southeast of the center.

The dithering patterns, exposure times, and number of exposures for each of the four core region fields (Table 2) were

<footnote n="33">33 NGVS fields are designated as NGVS $\pm x \pm y$. Field NGVS+0+0 is the field containing (in its northwest quadrant) M87, and x and y are numbers roughly representing the degrees of separation of a specific field (+ for east/north) and – for west/south), from NGVS+0+0. The core region comprises fields NGVS+0+0, NGVS+0+1, NGVS-1+0, and NGVS-1+1.</footnote>
<table><caption>**Table 2**
Exposure Times and Observing Strategy for the Core Regions Fields</caption><thead><tr><th rowspan="2">Filter</th><th colspan="2">Short Exposures</th><th colspan="4">Long Exposures (Global Background)</th><th colspan="2">Long Exposures (Elixir-LSB)</th></tr><tr><th>Exp. Time<br>(s)</th><th>Exp. #</th><th>Exp. Time<br>(s)</th><th>Exp. #</th><th>Point-Source Limit<br>(mag)</th><th>Extended-Source Limit<br>(mag arcsec<sup>-2</sup>)</th><th>Exp. Time<br>(s)</th><th>Exp. #</th></tr></thead><tbody><tr><td>(1)</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>u*</td><td>250</td><td>5</td><td>6402</td><td>11</td><td>26.3</td><td>29.3</td><td>4646</td><td>8</td></tr><tr><td>g</td><td>60</td><td>5</td><td>3150</td><td>5</td><td>25.9</td><td>29.0</td><td>3170</td><td>5</td></tr><tr><td>r</td><td>45</td><td>5</td><td>4809</td><td>7</td><td>25.3</td><td>27.2</td><td>...</td><td>...</td></tr><tr><td>i</td><td>40</td><td>5</td><td>2055</td><td>5</td><td>25.1</td><td>27.4</td><td>2055</td><td>5</td></tr><tr><td>z</td><td>65</td><td>5</td><td>4400</td><td>8</td><td>24.8</td><td>26.0</td><td>4400</td><td>8</td></tr></tbody></table>

Note. The table lists exposure times and number of frames obtained for the short exposures (designed to recover the centers of galaxies that saturate in the long exposures, columns 2 and 3), the long exposures (used for object detection and characterization, columns 4–7), and the lower resolution long exposures that were obtained at a later stage using the Elixir-LSB strategy (used to recover the surface brightness and large-scale structural parameters of galaxies on scales larger than a few arcminutes, columns 8 and 9). The exposure times (columns 2, 4, and 8) refer to the total integration time obtained in each filter (listed in column 1) and are the same for every field. The total exposure time is divided equally among the number of (dithered) exposures given in columns 3, 5, and 9. The point-source limit listed for the long exposures (column 6) refers to 10σ detections in *g*, *r*, *i*, and 5σ detections in *u**, *z*. The extended-source limit (column 7) refers to 2σ detections above the sky. For the global background stacks, the surface brightness limit is only applicable to scales less than a few arcminutes.

identical to those adopted for the full NGVS survey; the point-source depth of these fields is therefore very representative of those of other fields throughout the cluster. Two sets of data, however, exist for the core fields: the first set was obtained in 2008 before the start of the full survey and used a standard dithering pattern (as opposed to the step-dither pattern described earlier) that does not allow us to apply the Elixir-LSB data-reduction pipeline. Only “local background” and “global background” stacks are available for these data (see NGVS-I Section 4.2). A second set of data was obtained in 2010; the image quality of this set is not as good (with seeing FWHM between 1"2 and 1"5, compared with 0"62–0"86 for the 2008 data), but the step-dither pattern was used and the data were processed with Elixir-LSB. Owing to their significantly better spatial resolution, the original (2008), global background-subtracted core region images are best suited for the study of point sources and galaxies with effective radii less than several tens of arcseconds, a scale over which the scattered light background component does not vary significantly (see Ferrarese et al. 2012). The Elixir-LSB stacks obtained in 2010, on the other hand, are ideal for the study of large-scale structures and the low-surface brightness haloes of bright galaxies, thanks to the accurate, real-time characterization of the sky that is not possible for the 2008 stacks. In the remainder of this paper, the 2008 stacks are used unless otherwise noted. The observing dates and image quality for all data acquired in the core region are given in Table 3.

### 3. Automated Identification of Low-mass, Low Surface Brightness Galaxies

The identification of low-mass galaxies was performed using a specifically designed code, VCands, the details of which are described in this section and summarized schematically in Figure 2, to which we will refer periodically. We note that VCands explicitly excludes galaxies brighter than $g \sim 16$ mag, because these cannot be accurately represented by the single-Sérsic component two-dimensional fits on which VCands relies (see Section 3.3). This limitation is easily overcome, however, because the VCC (Binggeli et al. 1985) already gives a complete catalog of brighter galaxies for most of the NGVS survey area. Beyond the VCC boundary, bright

galaxies can be easily identified spectroscopically (e.g., Kim et al. 2014) or based on a visual inspection.

We took a two-pronged approach to assess the reliability and effectiveness of VCands. First, a training set of bona fide Virgo members in the core region was used to fine-tune and test the code (Section 3.1). The robustness of VCands was further tested using data from four control fields, a catalog of spectroscopic redshifts, and cross correlation with existing catalogs (see Section 3.4). Second, an extensive set of simulations allowed us to assess the completeness of our catalog, as well as any potential biases and systematics in the photometric and structural parameters recovered by VCands (Section 4).

VCands has proven to be an invaluable tool in the search for Virgo members. The core region fields contain about 1 million objects (to a $2.0\sigma$ detection threshold above the background), most of them foreground stars and background galaxies. VCands allows us to reduce the number of objects that could, potentially, be members of the cluster by over a factor of 500 compared with a nonoptimized SExtractor run, to ~1500 (see Sections 3.2 and 3.3). A final visual inspection (see Section 3.4) is necessary to identify the bona fide Virgo members among these potential candidates but is not an overly time-consuming task thanks to VCands’s initial downselect.

#### 3.1. Visual Definition of a Training Set of Bona Fide Virgo Cluster Members

The core region served as a test bed for our detection algorithm (Sections 3.2 and 3.3) and membership criteria (Section 3.4). The area contains 281 galaxies deemed to be certain or probable cluster members in the VCC, Impey et al. (1988), Trentham & Hodgkin (2002), Trentham & Tully (2002), Sabatini et al. (2003), Lieder et al. (2012), Kim et al. (2014), or Mihos et al. (2015); we will show that 31 of these are in fact either background sources or spurious detections (Appendix A). As one of the criteria to assess membership, we maintain a live catalog of objects with measured systemic velocities throughout the area covered by the NGVS. The catalog includes velocities from the NASA/IPAC Extragalactic Database (NED), the VCC, and the Data Release 10 of the
<table><caption>**Table 3**
Average Image Quality and Observing Dates</caption><thead><tr><th rowspan="2">Field</th><th rowspan="2">Filter</th><th colspan="2">Short Exposures</th><th colspan="2">Long Exposures (Global Background)</th><th colspan="2">Long Exposures (Elixir-LSB)</th></tr><tr><th>Seeing FWHM<br>(arcsec)</th><th>Obs. Date</th><th>Seeing FWHM<br>(arcsec)</th><th>Obs. Date</th><th>Seeing FWHM<br>(arcsec)</th><th>Obs. Date</th></tr><tr><th>(1)</th><th>(2)</th><th>(3)</th><th>(4)</th><th>(5)</th><th>(6)</th><th>(7)</th><th>(8)</th></tr></thead><tbody><tr><td>NGVS+0+0</td><td>u*</td><td>1"01</td><td>2008 Apr 2</td><td>0"80</td><td>2008 Mar 31</td><td>1"42</td><td>2010 Feb 18, Mar 16, Mar20, Apr 8, May 13, Jun 10</td></tr><tr><td>NGVS+0+1</td><td>u*</td><td>1"12</td><td>2008 Apr 2</td><td>1"09</td><td>2008 Apr 2</td><td>1"41</td><td>2010 Feb 16, Feb 18, Mar 20, May 13, Apr 8, Apr 11, Jun 10</td></tr><tr><td>NGVS-1+0</td><td>u*</td><td>0"74</td><td>2008 May 9</td><td>0"88</td><td>2008 May 9</td><td>1"31</td><td>2010 Feb 16, Feb 18, Mar 16, Mar 20, Apr 11, Apr 20, May 13, Jun 10</td></tr><tr><td>NGVS-1+1</td><td>u*</td><td>1"00</td><td>2008 Apr 1</td><td>0"81</td><td>2008 Apr 1</td><td>1"27</td><td>2010 Feb 16, Feb 18, Mar 20, May 13, Apr 8, Apr 11, Jun 10</td></tr><tr><td>NGVS+0+0</td><td>g</td><td>0"72</td><td>2008 Mar 6</td><td>0"62</td><td>2008 Mar 6</td><td>1"22</td><td>2010 Jan 13, Feb 14, Feb 17</td></tr><tr><td>NGVS+0+1</td><td>g</td><td>0"60</td><td>2008 Mar 9</td><td>0"63</td><td>2008 Mar 9</td><td>1"36</td><td>2010 Jan 13, Feb 14, Feb 17</td></tr><tr><td>NGVS-1+0</td><td>g</td><td>0"76</td><td>2008 Mar 8</td><td>0"86</td><td>2008 Mar 8</td><td>1"24</td><td>2010 Jan 13, Feb 14, Feb 17</td></tr><tr><td>NGVS-1+1</td><td>g</td><td>0"80</td><td>2008 Mar 5</td><td>0"85</td><td>2008 Mar 5</td><td>1"13</td><td>2010 Jan 13, Feb 14, Feb 17</td></tr><tr><td>NGVS+0+0</td><td>r</td><td>0"67</td><td>2008 Mar 5</td><td>0"77</td><td>2008 Mar 5/14</td><td>...</td><td>...</td></tr><tr><td>NGVS+0+1</td><td>r</td><td>0"64</td><td>2008 Mar 2</td><td>0"64</td><td>2008 Mar 8</td><td>...</td><td>...</td></tr><tr><td>NGVS-1+0</td><td>r</td><td>0"54</td><td>2008 Jun 1</td><td>0"67</td><td>2008 Jun 1</td><td>...</td><td>...</td></tr><tr><td>NGVS-1+1</td><td>r</td><td>0"97</td><td>2008 Apr 3</td><td>0"98</td><td>2008 Apr 3</td><td>...</td><td>...</td></tr><tr><td>NGVS+0+0</td><td>i</td><td>0"53</td><td>2008 Mar 3</td><td>0"54</td><td>2008 Mar 3</td><td>1"33</td><td>2010 Feb 7, Feb 10, Feb 20, Mar 9, May 13</td></tr><tr><td>NGVS+0+1</td><td>i</td><td>0"76</td><td>2008 Mar 8</td><td>0"68</td><td>2014 Mar 7/8</td><td>1"28</td><td>2010 Feb 7, Feb 10, Feb 20, Mar 9, May 13</td></tr><tr><td>NGVS-1+0</td><td>i</td><td>0"64</td><td>2008 Mar 8</td><td>0"63</td><td>2008 Mar 8</td><td>1"46</td><td>2010 Feb 7, Feb 10, Feb 16, Feb 20, Mar 9, May 13</td></tr><tr><td>NGVS-1+1</td><td>i</td><td>0"69</td><td>2008 Mar 5</td><td>0"75</td><td>2008 Mar 5</td><td>1"55</td><td>2010 Feb 7, Feb 10, Feb 16, Feb 20, Mar 9, May 13</td></tr><tr><td>NGVS+0+0</td><td>z</td><td>1"04</td><td>2008 Mar 1</td><td>0"97</td><td>2008 Mar 1</td><td>1"31</td><td>2010 Mar 9, Mar 12, Mar 20, Apr 7, Apr 8</td></tr><tr><td>NGVS+0+1</td><td>z</td><td>0"94</td><td>2008 Mar 1</td><td>1"02</td><td>2008 Mar 1</td><td>1"28</td><td>2010 Mar 9, Mar 12, Mar 20, Apr 7, Apr 8</td></tr><tr><td>NGVS-1+0</td><td>z</td><td>0"51</td><td>2008 Jun 12</td><td>0"63</td><td>2008 Jun 12</td><td>1"26</td><td>2010 Mar 9, Mar 12, Mar 17, Mar 20, Apr 7, Apr 8</td></tr><tr><td>NGVS-1+1</td><td>z</td><td>1"05</td><td>2008 Mar 1</td><td>1"05</td><td>2008 Mar 1</td><td>1"25</td><td>2010 Mar 9, Mar 12, Mar 17, Mar 20, Apr 7, Apr 8</td></tr></tbody></table>

Note. For each field (column 1) and filter (column 2), columns 3, 5, and 7 give the seeing FWHM, averaged across the full 1° stacked image, for the short exposures, the long exposures, and the Elixir-LSB long exposure, respectively (see Section 2 and Table 2). Columns 4, 6, and 8 give the date(s) when the observations were taken.
<figure><img src="image_3.png" /><figcaption>**Figure 2.** A schematic representation of *VCands*, from image preprocessing (steps A to C), to object detection and culling (steps D and E), to the estimation of membership probability (steps F to H) and final visual inspection (step J). See Section 3 for details.</figcaption></figure>

SDSS and is being supplemented and updated with data from our own follow-up programs at the Multiple Mirror Telescope (MMT), Keck, and Anglo Australian Telescope (AAT; E.W. Peng et al. 2019, in preparation; R. Guhathakurta et al. 2019, in preparation). Of the 281 galaxies in the Virgo core region, 85 are spectroscopically confirmed cluster members (Figure 1). To first order, therefore, there already exists a reference catalog of known Virgo members; however, this does not push nearly as deep down the luminosity function as we expect to probe with the NGVS data; for instance, the detection limit for the VCC is $M_g \sim -11.5$ mag, while Kim et al.'s spectroscopically confirmed catalog of Virgo members reaches $M_g \sim -12.6$ mag. These limits are 4–5 mag brighter than the galaxies we expect to be able to detect in the NGVS data.

To address this issue, three NGVS team members (L.F., P.-A.D., and P.R.D.) embarked, independently of each other, on a visual inspection of the core region that led to a catalog of bona fide Virgo members. Each team member had at his/her disposal images in all bands, both at full resolution and binned to varying degrees, as well as composite color images, but no redshift information or prior knowledge of membership. Membership was assessed based on colors, size, and surface

brightness, as well as morphology (in particular concentration and presence of substructure). Although the details on how to use the information were left to the individuals, the driving criterion was the same as that successfully employed in most previous surveys (with the exception of Kim et al., who required spectroscopic confirmation) and is essentially based on the fact that at comparable magnitude, galaxies in Virgo are expected to be more extended (or, equivalently, have lower surface brightness) than galaxies in the background. Furthermore, as noted by Trentham & Hodgkin (2002), low-mass galaxies in Virgo are not expected to have a regular spiral structure or a clear bulge/disk morphology: these are characteristics of more massive systems and therefore, when seen in a fainter, smaller galaxy, likely suggest that the object is at a larger distance. However, low-mass galaxies can have either smooth or irregular morphologies, with the latter generally associated with bluer colors and recent star formation. We note that the image quality of the NGVS (0.′′55 median seeing in the *i*-band) presents a significant advantage over the VCC or any other existing surveys, which generally report median seeing ~1.′′5, in distinguishing morphological traits.
<figure><img src="image_4.png" /><figcaption>**Figure 3.** A 4000 × 4000 pixel (12.5 × 12.5) region located in field NGVS-1+1 and centered approximately 14'16" west and 13'50" north of M87. Panel A shows the g-band image, smoothed with a 3 pixel Gaussian kernel for the purpose of illustration (the analysis described in the text always uses full-resolution images). The yellow rectangle, expanded in Figure 4, is centered on a low-mass, previously unidentified galaxy likely belonging to the Virgo cluster (R.A. = 12°29′m53.8′s, decl. = +12°37′14.6′s, J2000). Panels B and C show, respectively, an estimate of the sky and a mask, produced as described in Section 3.2. Panel D shows a background-subtracted, masked, ring-filtered image (Section 3.2). Finally, panels E and F show, respectively, all source detections obtained by running SExtractor using the original (panel A) and ring-filtered (panel D) image as the detection image. In both panels, the detections are identified by ellipses with semimajor axis, ellipticity, and position angle returned by SExtractor.</figcaption></figure>

There was very good agreement between the catalogs produced by the three team members, despite the subjectivity inherent to the process, and there was consensus as to the final catalog. Galaxies were divided—somewhat subjectively—into three classes according to the degree of confidence in their Virgo membership: class 0 are *certain* members; class 1 are *likely* members, and class 2 are *possible* members.34 The final visual catalog contained 396 objects and was used as a training set to optimize the automated selection of Virgo members (Sections 3.2 and 3.3). As detailed in Section 3.4, *VCands* successfully detected all but 23 of these galaxies (for $g > 16$ mag), although the latter were recovered during the visual inspection that is part of the follow-up to *VCands*. In addition, *VCands* detected eight galaxies that, a posteriori, were judged to be bona fide Virgo members but were not included in the training set, leading to a final catalog of 404 objects.

## 3.2. Detections and Initial Cuts

The main obstacle in detecting low-mass (and therefore, as a general rule, low surface brightness) galaxies in the NGVS fields (or any crowded field) is contamination from brighter,

higher surface brightness objects, in particular foreground stars, compact background galaxies, and globular clusters associated with bright Virgo galaxies. This is illustrated in Figure 3. Panel A shows a 12.5 × 12.5 region located approximately 14'16" west and 13'50" north of M87, at the center of which is a low surface brightness galaxy that, based on its appearance and structural parameters, is a good candidate for a low-mass galaxy belonging to the Virgo cluster (see Section 3.1). A SExtractor run (Bertin et al. 2002) on this cutout (that represents only about 4% of an entire MegaCam field) typically produces ~12,000 detections (Figure 3, panel E), depending on the choice of parameters, but will generally fail to detect the galaxy of interest. Figure 4, which shows a 4× zoom of the region shown in Figure 3, reiterates these points. The surface brightness disparity between the contaminants and the target low surface brightness galaxy prevents the latter from being detected as an independent object: this is a fundamental limitation, as large low surface brightness galaxies with scales comparable to the grid over which the background is estimated will be folded into the background, while smaller galaxies will be fragmented in multiple irregular sections, each associated with a brighter contaminant. We note that while it is possible to optimize SExtractor for the detection of a specific galaxy type (for instance, by using a filter designed specifically to represent its surface brightness profile, combined with appropriate choices of the parameters controlling deblending and the

<footnote n="34">34 Finding charts for all objects will be presented in a later section (Section 3.4), but the difference among the three classes can be appreciated, for instance, by comparing Figures 15(a), 16(a), and 17(a).</footnote>
<figure><img src="image_5.png" /><figcaption>**Figure 4.** A 3′.1 × 3′.1 zoomed-in version of the cutout shown in Figure 3. Panel A shows the g-band image, smoothed with a 3 pixel Gaussian kernel for the purpose of illustration. Panels B and C correspond to panels E and F of Figure 3, respectively, and show all source detections obtained by running *SExtractor* using the original (B) and ring-filtered (C) image as the detection image. The latter detections are also shown superimposed on the ring-filtered image in panel D. The sources detected by the two *SExtractor* runs can be compared directly in panel E: the large number of high surface brightness sources in the frame prevent *SExtractor* from identifying the target galaxy; by suppressing these sources, the galaxy is readily identified in the ring-filtered image. See Section 3.2 for further details.</figcaption></figure>

background estimate), the same parameters will not generally be appropriate for the detection of other potential Virgo candidates that—simply based on the fact that galaxies define nonhomologous scaling relations—will necessarily be described by different structural parameters. The weakness of such an approach is demonstrated in Davies et al. (2016), where a specifically optimized *SExtractor* run led to a highly incomplete catalog of objects with structural parameters biased to such an extent to render the catalog essentially unusable (Appendix B).

The solution adopted by the NGVS consists of processing the images—prior to running *SExtractor*—to reduce the contribution of the incriminating contaminants. After extensive experimentation, it was found that application of a circular ring filter (Secker 1995) produces the desired effect. The filter is selected to have inner radius equal to the median seeing FWHM of the image and 5 pixel width; its effect is essentially to replace objects that have scale lengths comparable to the seeing FWHM (the inner radius of the ring) with an estimate of the local background value, defined as the median within the ring. To further aid the detection, a mask is applied to the image prior to running the ring filter (step A in Figure 2). The mask is created by performing a *SExtractor* run on the images and selecting from the output catalog bright objects belonging to the stellar sequence, bright globular clusters (identified based on a combination of size, magnitude, and

proximity to bright Virgo galaxies), as well as artifacts; a common selection criterion for all objects is small size (estimated using the effective radius measured by *SExtractor*). This ensures that extended objects or intrinsically compact objects blended with more diffuse objects are not masked. *SExtractor* is then run in *ASSOCIATION* mode using the thus selected object list as input; the (appropriately rescaled) resulting segmentation file is used as a mask file. To this are added bright stars, including stellar haloes and diffraction spikes of saturated objects, identified using the *AUTOMASK* package that is part of the *THELI* pipeline (Dietrich et al. 2007; Erben et al. 2009). A local background, determined in a 128 pixel (24") grid using *SExtractor*, is subtracted (step B in Figure 2), and, finally, the ring filter is applied (step C in Figure 2). *SExtractor* is then run in “dual image mode,” using the ring-filtered image as the detection image, while the photometry is performed on the original image (step D in Figure 2).<fnref n="35" /> The result is shown in panel F of Figure 3 and panels C and D of Figure 4; all objects detected in the ring-filtered image (shown in panel D of Figures 3 and 4)

<footnote n="35">³⁵ All *SExtractor* runs use a weight map (*SExtractor WEIGHT_TYPE=MAP_RMS*) giving the inverse square of the $1\sigma$ errors at each pixel, accounting for both the contribution to each pixel from the individual images used in constructing the final stack and Poisson noise due to sources in the images themselves. When *SExtractor* is run on a ring-filtered image, the ring filter is also applied to the corresponding error map.</footnote>
<figure><img src="image_6.png" /><figcaption>**Figure 5.** Left: Σ, plotted against *Isophotal Area* for all g-band detections based on a conventional *SExtractor* run in field NGVS-1+1 (see Section 3.3), for a total of 211,413 objects. Right: Same diagram as in the left panel, but now showing all objects detected in an optimized *SExtractor* run using a ring-filtered image for object detection and the original images for the photometry, producing a much reduced number of detections (17,548). The pink, orange, and red circles locate *possible*, *likely*, and *certain* Virgo cluster members, respectively, identified based on a visual inspection of the images and detected by the code. For comparison, the same circles are reproduced in the left panel, although none of these objects is detected. By comparing the two panels, it is immediately clear that a conventional *SExtractor* run on the original images fails to detect objects in the region of parameter space that is occupied by Virgo low surface brightness galaxies. Points below the violet and to the left of the green dashed lines shown in the panel to the right are rejected when looking for cluster members. The two lines are defined as $y = 0.15x + 0.1$ and $y = (4 - \log \alpha^2)x - 7.7$, respectively, where $\alpha$ is the average seeing FWHM, in pixels.</figcaption></figure>

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /><figcaption>**Figure 6.** Σ, plotted against *Isophotal Area* for all g-band detections based on a *SExtractor* run on a ring-filtered image for one of the NGVS background fields, NGVS-BG1 (see Section 3.2). Comparing this figure to the right panel of Figure 5 shows that low surface brightness galaxies are indeed separated from background/foreground contaminant for this particular choice of parameters, as objects with large Σ and/or large *Isophotal Area* are absent in the background field.</figcaption></figure>

are identified by red ellipses. Because of the combination of masking and ring filtering, the number of detections is now vastly suppressed—by over an order of magnitude—compared with the case in which *SExtractor* is run directly on the original image. One of the detections, however, is the putative

<figure><img src="image_9.png" /><figcaption>**Figure 7.** The compartmentalization of the Σ vs. *Isophotal Area* plot for field NGVS-1+1 into 26 × 5 sections (a to z from right [large *Isophotal Area*] to left and 1 to 5 from bottom [low Σ] to top). The numbers in the legend identify the total number of detections in each section and (in parentheses) the number of visually identified *possible*, *likely*, or *certain* Virgo members in the same section. The Virgo membership probability $\phi$ (see Figure 12) is defined in part based on the ratio between the number of bona fide Virgo members (from the training set, Section 3.1) and the total number of objects detected by VCands within the same section (see Section 3.3).</figcaption></figure>

Virgo low-mass galaxy at the center of the field, entirely missed in the *SExtractor* run carried out on the unfiltered stacks. We will show in the next section that this procedure
<figure><img src="image_10.png" /><figcaption>Figure 8. An example of GalFit output for NGVS J12:29:53.78+12:37:17.9, the galaxy shown in Figures 3 and 4. The galaxy falls in the a2 section shown in Figure 7. The top panel shows the mask applied prior to running GalFit; the same mask, which includes all objects masked in any band, was used for all filters. The other panels show the image (top row), GalFit model (middle row), and residual image (image - model, bottom row) for (from left to right) the u'-, g-, r-, i-, and z-band images of the galaxy.</figcaption></figure>

proves effective in detecting low-mass galaxies across a large range of luminosities and structural parameters.

The procedure is repeated for all filters, using the g-band ring-filtered images for the detection and the original image (in each band) for the photometry. The g-band is used for object detection because it is slightly deeper than the other bands and has superb image quality (comparable to the r- and i-bands, see Tables 2 and 3). Although the r-band has similar properties, we refrain from using it for object detections for homogeneity with the rest of the survey, because r-band images are not available for the full NGVS area (see NGVS-I).

A SExtractor run on an (unfiltered) 1 deg² g-band NGVS image will generate ~250,000 detections (the exact number varying slightly from field to field). A SExtractor run on the same ring-filtered and masked image will generate ~17,000 detections, or ~70,000 detections across the entire core region. Of these, only ~0.5% are likely to be galaxies belonging to the Virgo cluster. As will be discussed in Section 3.4, visual inspection of the candidate galaxies is

ultimately necessary to assess Virgo membership; luckily, this task need not be performed on 70,000 objects (or, worse, a quarter of a million) because there are automated criteria that can be used to further narrow down the list of potentially promising candidates.

The first such criterion is based on a diagnostic plot designed to separate potential Virgo galaxies from background/foreground contaminants (step E in Figure 2). Extensive experimentation led us to choose the diagnostic plot shown in Figure 5. On the abscissa, *Isophotal Area* is SExtractor's *ISO0* parameter, that is, the area enclosed within the isophote corresponding to 2.4σ of the background rms (our adopted *ANALYSIS_THRESHOLD* and *DETECT_THRESHOLD*). On the ordinate, Σ is defined as

$$ \Sigma = \frac{F(\text{max}) \times \langle F(\text{ISO0}) \rangle}{F(\text{thresh})} \propto \frac{10^{-0.4\text{MU\_MAX}} \times [10^{-0.4\text{MAG\_ISO}/\text{ISO0}}]}{10^{-0.4\text{MU\_THRESH}}}, \quad (1) $$
<figure><img src="image_11.png" /><figcaption>**Figure 9.** Location of NGVS J12:29:53.78+12:37:17.9 (Figure 8) in scaling relations showing total g-band magnitude against (from left to right) Sérsic index *n*; geometric effective radius *r*<sub>e,geom</sub>, defined as the effective radius multiplied by √1 − *ϵ*, where *ϵ* is the galaxy ellipticity; central surface brightness *µ*<sub>0</sub>, and average surface brightness measured within one effective radius ⟨*µ*<sub>e</sub>⟩. All parameters are measured in the g-band and determined from the best-fitting GalFit model as described in Section 3.3. Magnitudes and surface brightnesses have been corrected for Galactic extinction. The solid curve shows the ridgeline of scaling relations defined by known VCC galaxies, extended to faint magnitudes by including known dwarf galaxies in the Local Group (P. Côtê et al. 2019, in preparation). The dashed lines correspond to the 1, 2, and 3σ scatter on the relations. The Virgo membership probability *ϕ* is based in part on the displacement of the objects under study from the main ridgeline of the magnitude vs. *n*, *r*<sub>e,geom</sub> and ⟨*µ*<sub>e</sub>⟩ relations (see Section 3.3 for details).</figcaption></figure>

where $F(\text{max}) \propto 10^{-0.4\text{MU\_MAX}}$ is the flux of the brightest pixel, $\langle F(\text{ISO0}) \rangle \propto 10^{-0.4\text{MAG\_ISO}/\text{ISO0}}$ is the average flux within ISO0, and $F(\text{thresh}) \propto 10^{-0.4\text{MU\_THRESH}}$ is the flux corresponding to 2.4σ of the background rms.

The behavior of extended objects within this diagnostic plot
can be understood through the following examples. Self-similar
objects (for instance, galaxies described by a Sérsic profile with
the same Sérsic index) with identical central surface brightness
[$F(\text{max})$], relative to the background rms) will move horizon-
tally toward the right of the diagram the more extended
(brighter) they are. On the other hand, self-similar objects with
identical total magnitude will move diagonally toward the
bottom right of the diagram the more extended (fainter central
surface brightness) they are. Finally, self-similar objects of the
same size will of course move vertically downward as they get
fainter. However, the magnitude of these shifts will depend on
the concentration of the object (i.e., on the Sérsic index $n$). The
effect is such that very concentrated objects, as they become
brighter, more extended, and/or of higher central surface

brightness, will tend to occupy a region of larger Σ and/or
smaller *Isophotal Area* compared with less concentrated
objects. Effectively, this causes objects of different magnitudes
to segregate in different areas of the diagram depending on
their concentration.

The left panel of Figure 5 shows all objects detected by a SExtractor run on the original (i.e., prior to applying the ring filter) g-band image for field NGVS-1+1, while the panel to the right shows all objects detected on a ring-filtered, masked image of the same field. A first striking difference between the two panels is the absence, in the catalog obtained using the ring-filtered images, of the thin, slanted sequence occupying the low *Isophotal Area* region of the panel to the left. This sequence is defined by point sources—the *Isophotal Area* increases with Σ (which correlates with total magnitude) because the former is measured *above* the background rms. The sharp bend at the top of the sequence is caused by the onset of saturation. Because the ring filter is effective in removing point sources, the sequence is not present in the panel to the right.
<figure><img src="image_12.png" /><figcaption>**Figure 10.** Photometric redshift estimates for NGVS J12:29:53.78+12:37:17.9, based on aperture magnitudes corrected for Galactic extinction and measured by SExtractor at radii equal to 6, 8, and 16 pixels (blue, green, and red points, respectively). The four panels show results using four different libraries, described in Section 3.3, with best-fitting models shown by the crosses. The measured photometric redshifts are listed in each panel for each set of aperture magnitudes, alongside the reduced χ² of the fit.</figcaption></figure>

The second striking difference is the presence of a smattering of points at large *Isophotal Areas* in the panel to the right, compared with the panel to the left. In each panel, galaxies that are deemed to belong to Virgo, based on the visual inspection described in Section 3.1, are shown as red, orange, and pink circles (for *certain*, *likely*, and *possible* Virgo members). It is immediately apparent that the SExtractor run on the original image fails to detect even a single cluster member, while a run on the ring-filtered image does produce positive identifications.

As a further confirmation of the effectiveness of our diagnostic plot in separating Virgo cluster members from background sources, Figure 6 shows objects detected in a ring-filtered, masked image of one of the four NGVS control fields, NGVS_BG1. There are a total of four such fields in the survey, located at three virial radii (~16°) from the cluster center, and at Galactic latitudes matching those of the lower and upper boundaries of the NGVS fields (see NGVS-I). The background fields are not expected to contain any Virgo members (although as we discovered, one might, as will be discussed in Section 3.4), and indeed by comparing Figure 6 to the right panel of Figure 5, it is immediately apparent that the Virgo field contains a smattering of objects at large *Isophotal Area* and a range of Σ that are absent in the control field.

In the right panel of Figure 5, galaxies with measured spectroscopic redshifts, $z_{\text{spec}}$, are marked as blue triangles

($z_{\text{spec}} < 0.1$) and green crosses ($z_{\text{spec}} \ge 0.1$). Point sources (stars or globular clusters) with $z_{\text{spec}} < 0.1$ are marked as blue crosses.<fnref n="36" /> The first noteworthy point is that all spectroscopically confirmed cluster members were identified as certain members in the visual inspection, despite the fact that velocity information was not used—by choice—during the classification. The second noteworthy point is that although background ($z_{\text{spec}} \ge 0.1$) objects and bona fide Virgo galaxies tend to occupy distinct locations in this diagram, their loci partially overlap, so that they cannot be cleanly separated. As a first, rough cut, we can, however, safely reject objects below the violet and to the left of the green dashed lines, defined as $y = 0.15x + 0.1$ and $y = (4 - \log \alpha^2)x - 7.7$, respectively, where $\alpha$ is the average seeing FWHM, in pixels, measured for each particular image (0.86 or 4.6 pixels for the image shown). The slopes of the two lines are roughly parallel to the lower boundary defined by the data and to the diagonal locus defined by the (mostly) background sources, while the intercept is chosen so that no known Virgo member is excluded by the cuts. These rather conservative cuts reduce the object list by ~40%, to 11,000, with the exact number varying slightly between fields. All of the objects surviving the cuts (for a total

<footnote n="36">³⁶ Note that objects must be detected by VCands to be shown in the figure. Because VCands is designed to select against point sources, the figure includes only a handful of spectroscopically confirmed stars and globular clusters. The number of such objects in the field is of course much larger.</footnote>
<figure><img src="image_13.png" /><figcaption>**Figure 11.** Location of NGVS J12:29:53.78+12:37:17.9 (Figure 8) in various color–color planes, based on *u*⁸⁻, *g*⁻, *r*⁻, *i*⁻, *z*-band magnitudes measured as part of VCands, the algorithm used to detect and identify low surface brightness galaxies belonging to the Virgo cluster (see Section 3). The diagnostic plot shown is used to apply a rough cut to the number of detections, mostly by identifying artifacts that have colors not reproducible by standard stellar population models. The colored squares show colors measured in different apertures (as shown in the legend) and corrected for Galactic extinction. The models (from Bruzual & Charlot 2003) assume an exponential star formation history and are shown for a range of ages (isochrones are shown by the gray dashed lines, with ages, in Gyr, as labeled along the top) and metallicities (shown by the colored lines). The blue points in the lower left corner of each panel show the change in colors due to Galactic reddening.</figcaption></figure>

of ~43,521 objects across the entire core region) are then further processed as described below.

### 3.3. Assigning Virgo Membership Probability

Since our membership criteria depend critically on having accurately measured structural and photometric parameters—more so than can be achieved with the SExtractor run described above—all potential Virgo members selected as described in Section 3.2 are subjected to a two-dimensional parametric fit using GalFit (Peng et al. 2002). Given the number of objects involved (over 40,000 in the core region), the procedure is extremely CPU intensive and was carried out using the Canadian Advanced Network for Astronomical Research (CANFAR, www.canfar.phys.uvic.ca), a cloud-based framework that allows easy access to very large resources for both storage and processing. All NGVS data (over 40 TB, including raw data and data products) are stored on CANFAR’s Virtual Observatory space, and VCands processing for the entire cluster has so far taken ~80 core-years, making the task impossible to carry out with conventional resources.

To allocate resources on CANFAR, the diagnostic plot discussed in Section 3.2 is divided into 130 regions defined, for practical reasons, to contain approximately the same number of sources. In Figure 7, which shows the case of field NGVS-1+1, these regions are enclosed within the slanted horizontal and vertical lines, with regions a,b,c,...z running approximately vertically from right to left, and regions 1,2,3,4,5 running approximately horizontally from bottom to top. In addition to the pragmatic reason related to the processing, this separation into regions is also useful to define our membership criteria: the ratio of the number of detections to the number of Virgo members in each region is one of the factors entering our definition of the Virgo membership probability, as discussed at the end of this section.

To derive the structural parameters used to define our membership criteria, three steps are performed for each detection: (1) a cutout is extracted centered on the object under investigation; (2) contaminants are masked; and (3) a two-dimensional parametric fit is performed. These steps are described in detail below.
<figure><img src="image_14.png" /><figcaption>**Figure 12.** Left: The Virgo membership probability $\phi$ for all VCands detections in the core region (green histogram, corresponding to the gray histogram in the right panel) and in the background fields (red histogram). Visually identified Virgo members are shown by the solid black histogram. Right: The Virgo membership probability $\phi$ for all objects detected in the Virgo core region. The gray shaded histogram shows all 21,781 objects detected by VCands and with GalFit parameters. The red, blue, and green histograms show possible (class 2), likely (class 1), and certain (class 0) Virgo cluster members, respectively, identified based on a visual inspection prior to running VCands, for a total of 313 objects. The black histogram shows all visually identified Virgo members, regardless of class. Finally, the black squares connected by the orange line show the purity of the sample, as a percentage, that is, the ratio of the number of Virgo members to the total number of VCands detections in each $\Delta\phi = 0.05$ bin (as indicated along the ordinate on the right-hand side). See Section 3.3 for further details.</figcaption></figure>

(1) Creating a cutout (step F in Figure 2). For each object, a square cutout is made of size equal to $12 \times r_e$, where $r_e$ is the effective radius measured by the SExtractor run described above (parameter FLUXRadius). This choice allows us to limit large-scale background variations within the region while still sampling well beyond the optical extent of the galaxy: for instance, for a galaxy described by a Sérsic profile with $n = 3$, less than 0.01% of the light is contained beyond 12 effective radii, with that fraction decreasing for smaller Sérsic indexes. Objects that fall less than $12 \times r_e$ from the edge of a field are excluded from further analysis, but care is taken to ensure that they are recovered in the neighboring field(s). To account for objects that might be in regions of variable background, for instance, galaxies in the haloes of larger Virgo galaxies, a global background, as measured by SExtractor, is subtracted if the background gradient across the cutout is larger than 40% of the average value.

(2) Masking contaminants (step G in Figure 2). A mask is created by adding to the already existing mask (described in Section 3.2) all objects present in the cutout, other than the one of interest. This is accomplished in an iterative process as follows. An initial mask is created by running SExtraction on the cutout, using the same weight image described in Section 3.2 but multiplied by an exponential profile, centered on the object of interest, with normalization and scale proportional to the magnitude and effective radius of the object as given by the initial SExtractor parameters. The exponential profile has the effect of “down-weighting” the target object by artificially lowering the S/N over its footprint, until it falls below SExtraction’s detection threshold. When run using this modified weight image, SExtractor should ideally detect every object in the frame, except for the one under investigation. This procedure is repeated in each band, and a mask—the same for every band—is created by including all objects detected in any band. To test that the mask does

indeed include all contaminants, we exploited a specific feature implemented in the Galaxy Analysis over Large Areas Parameter Assessment by GalFitting objects from SExtractor (GALAPAGOS, Barden et al. 2012). While originally designed to detect and measure simultaneously multiple objects in a given image, we instead take advantage of GALAPAGOS’s high dynamic range mode of object detection. In this mode, GALAPAGOS performs a “cold” SExtractor run designed to pick up brighter and larger objects and a second, “hot” run designed to detect fainter sources. GALAPAGOS then adds to the cold source catalog all hot detections that do not fall inside the Kron ellipse of a cold source. For our application, we consider our mask to be successful if GALAPAGOS produces only a single cold and single hot detection, both associated with the object of interest. If any other combination of cold and hot sources is returned, a new mask is produced by slightly adjusting the initial parameters—including, for instance, a small shift in the object’s center (no larger than the seeing FWHM), a change in the size of the cutout, or an adjustment of the exponential normalization and/or scale of the profile by which the weight image is multiplied. The entire procedure is repeated with the new mask until GALAPAGOS produces a single cold and a single hot detection.

(3) Two-dimensional fits (step H in Figure 2). To obtain a more refined characterization of the object of interest, the cutout is then processed with GalFit, using the final mask obtained as described above, and the cold GALAPAGOS parameters as initial guesses. In all cases, we only allow for a single-Sérsic model and a tilt in the background fit (if deemed necessary based on an analysis of a rough sky measurement in the four corners of the cutout). The use of a single-Sérsic model is not an unreasonable choice, as most of our galaxies are low-mass, morphologically simple systems (recall that bright galaxies are excluded from the onset). The exception are nucleated galaxies. These are usually identifiable because the
<figure><img src="image_15.png" /><figcaption>Figure 13. All galaxies detected in the core region based on NGVS images. Red ellipses identify VCC galaxies, while green ellipses identify non-VCC galaxies detected in previous studies (Trentham & Hodgkin 2002; Trentham & Tully 2002; Sabatini et al. 2003; Lieder et al. 2012; Kim et al. 2014 and Mihos et al. 2015). Blue ellipses are new NGVS detections. The ellipticity and position angle of the ellipses correspond to those measured for the galaxies in the NGVS images, with the semimajor axis equal to 10 times the measured effective radius.</figcaption></figure>

presence of the nucleus generally biases the Sérsic index to a value larger than expected given the size/brightness of the galaxy. When this happens, the center is masked and GalFit is run again, still using a single-Sérsic component. The cutout, GalFit model, and residual are shown in Figure 8 in the case of a specific galaxy, NGVS J12:29:53.78 +12:37:17.9, the same galaxy shown in Figures 3 and 4. For about 1000 objects, GalFit fails to converge; the galaxies for which this happens are flagged and visually inspected at a later stage (Section 3.4).

At this stage of the process, we are ready to estimate the likelihood that a given galaxy is a member of the cluster (step I in Figure 2). A Virgo membership probability $\phi$, is computed as the product of a number of independent “distance indicators,” each weighted such that $\phi$ is maximized for the members of the training set of bona fide Virgo members:

$$ \phi \propto \phi_{\Sigma} \times (\phi_n \times \phi_{r_e} \times \phi_{\langle \mu_e \rangle}) \times \phi_{z_{ph}} \times (\phi_{\text{blend}} \times \phi_{\text{streak}}). \quad (2) $$

The weights are determined based on a complex set of conditions and decision trees and vary according to factors ranging from the magnitude of the object and the reliability with which its structural parameters are measured, to the proximity of the object to bright, saturated stars. The factors contributing to $\phi$ are described below; each is constrained to be less than or equal to 1 and larger than 0, with the exact lower bound depending on the factor in question as well as the specifics of the galaxy being investigated:

1. The variable $\phi_{\Sigma}$ is a factor based on the object's location in the $\Sigma$ versus IsophotalArea plane (see Section 3.2, Figure 7). This factor is defined as

$$ \min(1.0, 0.5 + 2.5N_{\text{Virgo}}/N_{\text{det}}), \quad (3) $$

where $N_{\text{Virgo}}$ is the number of bona fide Virgo members (from the training set, Section 3.1) falling in the same section as the object for which $\phi$ is being measured and $N_{\text{det}}$ is the total number of objects detected by VCCands in the same section. $\phi_{\Sigma}$ is constrained to be larger than 0.5 and less than 1.0.

2. The variables $\phi_n$, $\phi_{r_e}$, and $\phi_{\langle \mu_e \rangle}$ are based on the scale parameters measured by GalFit: Sérsic index $n$, effective radius $r_e$, and the average surface brightness within the effective radius $\langle \mu_e \rangle$. Each factor is computed as the distance of the object from the ridgeline of the scaling relation between each of the above parameters and total magnitude (see Figure 9):

$$ \phi_x = 1/(\sqrt{2\pi} e^{\Delta x^2/2}). \quad (4) $$

In the expression, $\Delta x$ is the object's distance from the ridgeline in units of the relation's $1\sigma$ scatter, $\sigma_x$ (dashed lines in Figure 9):

$$ \Delta x = [\log(x) - \log(x_0)]/\sigma_x \quad \text{for } x = n, r_e; \quad (5) $$

$$ \Delta x = [x - x_0]/\sigma_x \quad \text{for } x = \langle \mu_e \rangle. \quad (6) $$

The lower bounds of $\phi_n$, $\phi_{r_e}$, and $\phi_{\langle \mu_e \rangle}$ are set equal to 0.1, 0.3, and 0.15, respectively.
<figure><img src="image_16.png" /><figcaption>**Figure 14.** All galaxies detected in the core region based on NGVS images. The galaxies are color coded according to their membership status: red for class 0 (certain members), blue for class 1 (likely members), and green for class 2 (possible members). The ellipticity and position angle of the ellipses correspond to those measured for the galaxies in the NGVS images, with the semimajor axis equal to 10 times the measured effective radius.</figcaption></figure>

3. The variable $\rho_{zph}$ is based on photometric redshifts (photo-z), estimated using LePhare (Arnouts et al. 1999; Ilbert et al. 2006) and a range of spectral libraries (Figure 10). Photo-z's are not accurate enough to secure membership for galaxies at the distance of Virgo (e.g., Raichoor et al. 2014) but can be used to select against sources that are clearly in the background. The complication is that none of the template libraries used in computing photo-z's include old, metal-poor stellar populations that are typical of the low-mass galaxies whose membership we are trying to establish. Using the COSMOS libraries included in the LePhare distribution results in some bona fide low-mass Virgo galaxies having extreme redshifts ($z \sim 2$). After some experimentation, we found that this was due to the inclusion, in the COSMOS libraries, of starburst templates. Removing these templates largely resolved the issue (the resulting templates are indicated as “COSMOSCUT” in Figure 10). We also adopted two additional sets of libraries, the first from Maraston & Strömbäck (2011) (“M11” in Figure 10) and the second by adding to the COSMOS libraries low-metallicity, old stellar population templates from Bruzual & Charlot (2003) (“COSMOSBC03” in Figure 10). The photo-z factor entering our computation of $\rho$ is an average of the photo-z's obtained using all four libraries, with weights optimized using the training set of Virgo members. The lower bound on $\rho_{zph}$ is set equal to 0.1.

4. Only in the case of objects for which the photo-z measurement fails, $\rho_{zph}$ is replaced by a factor based on the initial colors measured by SExtractor. This criterion is used primarily to reject artifacts, many of which have colors that cannot be reproduced by stellar population models. An example of the diagnostic plot used for this purpose is shown in Figure 11 for a bona fide Virgo member, NGVS J12:29:53.78+12:37:17.9. The various colored squares show colors measured in different apertures (using SExtractor and corrected for Galactic extinction). The models (from Bruzual & Charlot 2003, although Maraston & Strömbäck 2011 models were also investigated) are shown for a range of average ages based on an exponential star formation history (MacArthur et al. 2004 isochrones are shown by the gray dashed lines, with ages, in Gyr, as labeled along the top) and metallicities (shown by the colored lines). More specifically, the weight assigned to an object is decreased (increased) if its colors are outside (inside) a wide (narrow) preset range. As an example, starting from a value of 0.5, the weight of an object is decreased if its $g-i$ color is outside the range [−0.6, 1.4] mag and increased if it is inside the range [−0.4, 1.2] mag. The amount by which the weight is changed depends on the color (as some colors are more robust than others when using stellar population models), on how far outside (inside) the range it is, and on how reliably the color is measured.
<figure><img src="image_17.png" /><figcaption>**Figure 15.** Finding charts for bona fide Virgo members classified as class 0 (certain members). In this and all subsequent figures, all galaxies are shown in the g-band, the images are smoothed using a 9 pixel width boxcar function (for visualization purposes only), and the galaxy is at the center of the field. The galaxies are arranged from top left to bottom right going from brighter to fainter g-band magnitudes, and the size of the cutout varies as a function of magnitude as follows: 750" for $g \le 11$ mag; 375" for $11 \le g < 13$ mag; 260" for $13 \le g < 15$ mag; 130" for $15 \le g < 17$ mag; 93" for $17 \le g < 19$ mag; 56" for $g \ge 19$ mag. The gray scale is also adjusted: the saturation level is $\mu_g = 25$ mag arcsec$^{-2}$ for $g < 17$ mag, $\mu_g = 27.5$ mag arcsec$^{-2}$ for $17 \le g < 19$ mag, and $\mu_g = 28.3$ mag arcsec$^{-2}$ for fainter galaxies. For each galaxy, we list the NGVS ID, the VCC ID (when available), the g-band magnitude (Table 5), and the systemic velocity (when available, in km s$^{-1}$, see Table 4).</figcaption></figure>
<figure><img src="image_18.png" /><figcaption>Figure 15. (Continued.)</figcaption></figure>

5. The variables $\rho_{\text{blend}}$ and $\rho_{\text{streak}}$ are meant to guard against the possibility that an object is an artifact, the two most common cases being a blend due to the ring filtering and

a streak (such as a diffraction spike or a satellite trail). Potential blends are identified as objects for which the difference between the initial SExtractor and final
<figure><img src="image_19.png" /><figcaption>Figure 15. (Continued.)</figcaption></figure>

GalFit effective radii and ellipticities exceed 50% and 30%, respectively; the larger the difference, the lower the $\rho_{\text{blend}}$. Potential streaks are identified as objects with axial

ratio, as measured by GalFit, larger than 0.4; for these objects $\rho_{\text{streak}}$ is lowered, with consideration also given to the robustness of the measurement. Additionally, objects
<figure><img src="image_20.png" /><figcaption>Figure 15. (Continued.)</figcaption></figure>

that could potentially be associated with stellar haloes are identified based on their proximity to a star included in the catalog used in the creation of the bright star mask

(Section 3.2). The latter information is only used indirectly in the calculation of $\phi$, as the weights for the factors entering $\phi$ are reduced for objects that are found
<figure><img src="image_21.png" /><figcaption>Figure 15. (Continued.)</figcaption></figure>

to be close to bright stars; $\rho_{\text{blend}}$ and $\rho_{\text{streak}}$ are constrained to be larger than 0.

We stress that the weights assigned to each of the factors entering $\rho$ are always larger than zero and defined in such a

way that no object can be rejected based on a *single* criterion (for instance, based on it not conforming to known structural scaling relations or failing our photometric redshift test). Rather, an object must fail several of the criteria described
<figure><img src="image_22.png" /><figcaption>Figure 15. (Continued.)</figcaption></figure>

above for its membership probability to be ranked low. In the case of the galaxy shown in Figures 8–10, all factors mentioned above, as well as $\phi$, are equal to 1.0.

The effectiveness of our definition of $\phi$ is shown in the left panel of Figure 12, which compares $\phi$ for all objects detected in the core region (green hatched histogram) and in the four
<figure><img src="image_23.png" /><figcaption>Figure 15. (Continued.)</figcaption></figure>

background fields (red hatched histogram). The core region
fields contain a significant population of objects with large φ
that are essentially absent in the background fields. Indeed, the

black histogram in the same figure shows bona fide Virgo
members belonging to our visual training set (Section 3.1),
making up the bulk of the high-φ population. The right panel of
<figure><img src="image_24.png" /></figure>

(h)

<caption>Figure 15. (Continued.)</caption>
<figure><img src="image_25.png" /><figcaption>**Figure 15.** (Continued.)</figcaption></figure>

the same figure further expands on this point. The filled gray histogram includes all 21,781 objects in the core region detected by VCands in regions 1–5 and a–u (see Figure 7) and with GalFit parameters, while the black histogram shows the subset of 313 objects belonging to our visual training set.<fnref n="37" /> The same 313 objects, divided according to their membership class, are shown by the color histograms. It is

immediately apparent from the figure that bona fide Virgo members occupy preferentially the high-$\phi$ region, while the bulk of the objects is skewed toward low $\phi$. To maximize efficiency, we opt to select for further visual inspection only candidates with $\phi \gtrsim 0.22$: this region contains only 6.6% of all detections, but 98% of all bona fide Virgo members. The black squares connected by the orange line show the “purity” of the VCands detections, that is, the ratio (expressed as a percentage) between the number of Virgo members in the training set and the total number of VCands detections, each measured in $\Delta\phi = 0.05$ bins. For $\phi \gtrsim 0.22$, the purity ranges from 1% to 95% and clearly correlates with $\phi$ (over 90% of all detections are Virgo members when $\phi > 0.85$), while for $\phi < 0.22$ the

<footnote n="37">³⁷ Note that our visual training set includes 396 galaxies; however, of these, 43 galaxies are too bright to be detected by VCands, 27 galaxies are not detected (generally because they fall within the masked halo of a bright star), and 13 galaxies are detected but the GalFit fit failed (mostly because the galaxy falls either in a problematic area or too close to the edge of the chip).</footnote>
<figure><img src="image_26.png" /><figcaption>**Figure 16.** As Figure 15(a), but for class 1 galaxies (likely members).</figcaption></figure>

purity is always lower than 0.1%, that is, fewer than 0.1% of all detected objects are members of the cluster. A cut at $\phi = 0.22$ therefore misses very few potential Virgo members, while

leading to a manageable data set for further visual inspection: 1446 objects over the entire core region. These are the objects taken forward to the next step.
<figure><img src="image_27.png" /><figcaption>**Figure 16.** (Continued.)</figcaption></figure>

### 3.4. Final Visual Checks

VCands detects and produces GalFit fits for 21,781 objects in the core region, 1446 of which have $\rho \gtrsim 0.22$. In

addition, there are 928 objects that are detected by VCands but for which GalFit fails to converge. All of the objects with $\rho \gtrsim 0.22$ or with a failed GalFit fit are visually inspected using a specifically designed Graphical User Interface, a task
<figure><img src="image_28.png" /><figcaption>Figure 16. (Continued.)</figcaption></figure>

requiring about 40 minutes for each square degree field (step *J* in Figure 2). At the end of the visual inspection, 323 bona fide Virgo members were identified among the candidates with

$\rho \gtrsim 0.22$ (i.e., 22.5% of the total number of detections) and 13 additional bona fide Virgo members among the candidates that were detected for which GalFit failed (1.4%; most of the
<figure><img src="image_29.png" /><figcaption>Figure 16. (Continued.)</figcaption></figure>

objects for which the fit fails turn out to be artifacts). During the visual inspection, the fields are also scanned for potential candidates that might not have been detected by VCCs, as

well as VCC galaxies brighter than $g \sim 16$ mag (i.e., in the range excluded by VCCs). Based on this visual inspection, we added 43 bright VCC galaxies (again, not meant to be
<figure><img src="image_30.png" /><figcaption>**Figure 16.** (Continued.)</figcaption></figure>

targeted by *VCands*) and 27 fainter galaxies that were not detected by *VCands* (at least not with $\rho \gtrsim 0.22$—only one of these is a VCC galaxy, VCC 1035, a $g = 16.1$ mag galaxy

deeply embedded within the halo of a bright saturated foreground star). Cross matching with the full *VCands* catalog of 21,781 sources shows that seven of these 27 galaxies were in
<figure><img src="image_31.png" /><figcaption>**Figure 16.** (Continued.)</figcaption></figure>

fact detected by VCands but have $\rho < 0.22$, implying that only ~0.03% of the objects with $\rho < 0.22$ are bona fide Virgo members. The total number of bona fide Virgo members within the core region is thus 323 (from VCands with $\rho \gtrsim 0.22$) + 13 (detected by VCands but for which GalFit failed) + 43 (bright VCC galaxies) + 27 (galaxies identified by eye but either not detected by VCands or detected with $\rho < 0.22$) = 406. Below we will explain that two of these galaxies have velocity slightly above our 3500 km s⁻¹ limit and will therefore be removed from the final catalog.

During the visual inspection, each candidate is assigned a “membership class,” with classes 0, 1, and 2 corresponding to *certain*, *likely*, and *possible* members. Background objects are classified as class 3 or 4 (depending on whether they “likely” or “certainly” belong to the background population), while artifacts are classified as class 5. We note that the classification is not just based on a visual impression drawn from images in a single band; rather, images in all bands as well as color images are inspected, and the parameters that go into calculating $\rho$ are also taken into account. Despite its subjective nature, adopting a classification scheme along the lines discussed above is commonly done: the VCC, for instance, classified galaxies as “M” or “P” for “certain” or “probable” members and “B” for background objects, while Trentham & Hodgkin (2002) and Trentham & Tully (2002) used a classification scheme similar to the one adopted in this paper. Of the 406 galaxies in the core region, 173 are classified as class 0, 104 as class 1, and 129 as class 2.

Five independent tests allow us to verify the effectiveness of our detection algorithm and classification scheme:

1. As discussed in Section 3.1, in the core region a visual search for potential Virgo members was carried out prior to running VCands and indeed used as a training set to optimize the algorithm. With the exception of the 27 (not detected or detected but with $\rho < 0.22$) and 13 (detected but not fitted) galaxies mentioned above, all visual candidates fainter than $g \sim 16$ mag were recovered by VCands (brighter candidates are already identified in the VCC). Based on the simulations described in Section 4, we expect the detection rate for VCands to plateau at ~90%; indeed, in the magnitude range $16 < g < 19$ (where the completeness is expected to be ~90%), 14 of the 113 bona fide Virgo members (i.e., just over 10%) in our final catalog were either not detected, or detected but not fitted, in agreement with the expectations from the simulations. We also checked the final VCands

classification against the one performed during the initial visual identification (Section 3.1), finding very consistent results.

2. The visual catalog that served as a training set included 396 galaxies. While VCands, followed by the visual inspection, recovers all of these galaxies, there are eight additional galaxies with $\rho \gtrsim 0.22$ that passed the visual inspection but were not included in our original training set. These galaxies are judged to be bona fide Virgo members (all are class 1 or 2) and demonstrate that VCands is capable of improving over a simple (but time-consuming) detection method based solely on visual inspection of the images.

3. We compiled a catalog of radial velocities for the entire NGVS footprint using data from the SDSS DR10, NED, and our own follow-up programs at the MMT, Keck, and AAT. All 85 galaxies with $v < 3500$ km s⁻¹ in the core region are identified as bona fide Virgo members in our catalog, and all but one are classified as class 0 (the exception is classified as class 1). However, two galaxies in our catalog have $v > 3500$ km s⁻¹: NGVS J12:30:15.99+13:18:27.6 ($v = 4434$ km s⁻¹, classified as class 1) and NGVS J12:31:20.29+11:31:49.4 ($v = 7623$ km s⁻¹, classified as class 2). These galaxies are excluded from our final catalog, leading to a total of 404 bona fide Virgo members.

4. As discussed in Section 3.2, VCands was also run on four background fields located at three virial radii (~16°) from the cluster center. The 619 VCands candidates with $\rho \gtrsim 0.22$ detected in these four fields were inspected exactly as done for the core region fields, and two bona fide Virgo members were identified, both belonging to NGVS_BG2 and both classified as class 0 (i.e., certain members). Cross matching with the spectroscopic catalog reveals that the two galaxies are indeed at a recessional velocity that is characteristic of Virgo members, $v = 549$ km s⁻¹ and $v = 3363$ km s⁻¹. Additionally, these are the only two galaxies with $v < 3500$ km s⁻¹ in all background fields. The VCands identification and further visual confirmation for these two galaxies are a strong validation of our procedure for assigning Virgo membership.

5. Certain galaxy types might elude detection. Among these are blue compact dwarfs (BCDs), which might be mistakenly identified as background sources due to their blue, compact appearance; irregular galaxies, whose
<figure><img src="image_32.png" /><figcaption>**Figure 17.** As Figure 16(a), but for class 2 galaxies (possible members). Note that for three unusually large (given their magnitude) galaxies (NGVS J12:29:20.27 +12:01:16.4, NGVS J12:27:15.01+12:50:55.9, and NGVS J12:26:55.95+12:59:40.0) the cutouts cover an area four times as large (187" × 187") as that for galaxies of comparable magnitude.</figcaption></figure>

Virgo membership probability $\phi$ might be biased low due to the presence of internal substructure that can lead to inaccurate GalFit parameters; and very low surface

brightness, extended galaxies, such as the UDGs recently detected in the Coma cluster (Koda et al. 2015; van Dokkum et al. 2015), for which $\phi$ might again be biased
<figure><img src="image_33.png" /><figcaption>Figure 17. (Continued.)</figcaption></figure>

low if the galaxies fall outside the range of the adopted scaling relations. Meyer et al. (2014) studied a nearly complete sample of BCDs, irregular and star-forming

Virgo galaxies, selected from SDSS images. Of the sample presented in their Tables 3 and 5, 35 galaxies fall within the NGVS footprint. These include irregular or
<figure><img src="image_34.png" /><figcaption>Figure 17. (Continued.)</figcaption></figure>

Sm-type star-forming galaxies, as well as BCDs. The latter vary in appearance, ranging from galaxies with nuclear star-forming regions surrounded by a regular low

surface brightness component, to galaxies with irregular star-forming regions surrounded by asymmetric envelopes. All of these galaxies were detected and fitted by
<figure><img src="image_35.png" /><figcaption>**Figure 17.** (Continued.)</figcaption></figure>

VCands, and all are classified as *certain* Virgo members. Additionally, a cross match between the NGVS catalog and the catalog of star-forming galaxies presented

by Voyer et al. (2014) based on *Galaxy Evolution Explorer (GALEX)* imaging shows that all star-forming Virgo cluster members detected by *GALEX* are included
<figure><img src="image_36.png" /><figcaption>**Figure 17.** (Continued.)</figcaption></figure>

in the NGVS catalog. As for the UDGs, the Coma UDGs listed by van Dokkum et al. (2015) fall within the $3\sigma$ envelope of our scaling relations and therefore should not

be penalized a priori by *VCands*. More extreme UDGs were detected by Mihos et al. (2015) in the Virgo cluster. Of their three galaxies (two of which are in the core
<figure><img src="image_37.png" /><figcaption>Figure 17. (Continued.)</figcaption></figure>

region), one was detected, but not fitted, by VCands, as expected based on the simulations to be described in Section 4 given their structural parameters. However, all

three galaxies were identified and added to the catalog based on our visual inspection of the images. We conclude that our procedure is effective in detecting
<figure><img src="image_38.png" /><figcaption>**Figure 17.** (Continued.)</figcaption></figure>

<figure><img src="image_39.png" /><figcaption>**Figure 18.** Finding charts for the two objects originally classified as class 1 (NGVS J12:30:15.99+13:18:27.6) and class 2 (NGVS J12:31:20.29+11:31:49.4) with an existing radial velocity measurement placing them beyond the nominal $v = 3500 \text{ km s}^{-1}$ cutoff adopted for Virgo.</figcaption></figure>

and assigning membership for all known galaxy types in the Virgo cluster.

Figure 12 shows the correlation between our final assigned membership (class 0, 1, and 2), and the membership probability $\phi$ for the 404 bona fide Virgo members comprising our final Virgo core catalog. All galaxies are identified in Figure 13 and color coded according to whether they had already been reported in previous work (red for VCC galaxies and green for galaxies identified in other surveys; see Appendix A). New NGVS detections are shown in blue. Figure 14 shows the same galaxies, but now color coded according to the membership class (red, blue, and green for class 0, 1, and 2, respectively). In both figures, the ellipse identifying each galaxy has ellipticity equal to the average value measured between 1'' and one effective radius,<fnref n="38" /> with the

semimajor axis equal to 10 times the effective radius, measured as described in Section 5. Finally, finding charts for all 404 bona fide Virgo members, divided into the three separate classes, are shown in Figures 15(a) to 18.

**4. Estimation of Completeness and Reliability of Recovered Parameters from Simulations**

The tests discussed above provide empirical evidence on the effectiveness of our approach in detecting low surface brightness galaxies and correctly assigning membership. To further characterize the sensitivity of our detection algorithm as a function of galaxy structural parameters, we carried out an extensive set of simulations, whereby simulated galaxies—convolved with the appropriate point-spread function (PSF) and with realistic noise properties—were injected into each of the core region frames, and then recovered using exactly the same procedure described in Section 3.

In total, 182,500 galaxies were generated—36,500 in each filter—under the assumption that their intrinsic light distribution follows a Sérsic profile. Galaxies were randomly generated

<footnote n="38">³⁸ Note that in some cases, the ellipse does not seem to be a good representation of the large-scale ellipticity and/or position angle of the galaxy. The reason is that one effective radius—within which the ellipticity is averaged—is on a scale 10 times smaller than shown, and, within this region, the brighter galaxies often display strong isophotal twists and ellipticity changes that are not visible in the images.</footnote>
to populate (but extend beyond) the scaling relations expected for Virgo members, with Sérsic indices, effective radii, and magnitudes in the range $0.4 < n < 2.5$, $0''9 < r_e < 53''$ ($75 \lesssim r_e \lesssim 4200$ pc), and $16.0 \lesssim m_g \lesssim 25.2$ mag (a color term was applied to derive magnitudes in $u^*$, $r$, $i$, and $z$; see Figures 19(a)–(e)). A Sérsic function is completely determined by these three parameters—*n*, $r_e$, and *m*—which can therefore be used to derive, analytically, surface brightness values (e.g., Graham & Driver 2005). The central, effective, and average (within one effective radius) surface brightnesses of our simulated galaxies thus cover the ranges (in the *g*-band and measured in mag arcsec$^{-2}$) $15.7 \le \mu_0 \le 33.0$, $19.5 \le \mu_e \le 34.4$, and $19.0 \le \langle \mu_e \rangle \le 33.4$, respectively. Apparent ellipticities and major axis position angles for the galaxies were randomly distributed (independently of all other parameters) in the range $0 \le \epsilon \le 0.65$ and $0 \le \text{PA} < 180^\circ$.

Galaxies were assigned R.A. and decl. to cover the entire region imaged by each of the core region frames (no effort was made to avoid crowded regions or bright galaxies). Each galaxy was then convolved with the PSF for the appropriate field, filter, and location within the frame, determined at the location of the galaxy center using an iterative, automated version of DAOPhot (Stetson 1987) that relies on SExtractor parameters (Bertin & Arnouts 1996) to identify a list of uncrowded stars across the field (see NGVS-I for details). Finally, Poisson noise was added, making sure to properly account for the sky background so that, once injected in the real frames, the noise properties of the simulated galaxies reflected those expected for real objects. Finally, the simulated galaxies were added to the real frames. No more than 100 galaxies at a time (equally spaced in R.A. and decl. but centered randomly within the given field) were added to each core region image (for the largest galaxies, a single galaxy was added) to avoid having them partially overlap with each other. New error maps were generated to account for the presence of the simulated galaxies. In total, over 500 images were generated for each filter, each containing between one and 100 simulated galaxies on top of the real frames and then processed exactly as described in Section 3.

The distribution of input parameters for the simulated galaxies is shown by the black histograms in Figures 19(a)–(e). The results do not differ appreciably among the four core region frames—not surprising because the frames are very similar in terms of (real) object density, depth, and image quality. Here and in all subsequent figures, we therefore do not distinguish between the four core region frames and only show the combined results for fields NGVS+0+0, NGVS+1+0, NGVS-1+0, and NGVS-1+1. The red histograms show the distribution of recovered parameters. Two points are worth noticing: (1) the recovery rate for simulated galaxies is never 100%: even for the brightest of the simulated objects ($g \sim 16$ mag), the number of galaxies detected and fitted (with GalFit) by VCands plateaus at $\sim 90\%$; and (2) while the detection rate declines gradually as the galaxy magnitude increases, the decline is far more abrupt in surface brightness: in the *g*-band, essentially all galaxies become undetectable once $\langle \mu_e \rangle$ becomes fainter than 29 mag arcsec$^{-2}$.

The first point is due to the fact that, in $\sim 10\%$ of the cases, the simulated galaxy will fall in a high surface brightness region, as is, for instance, found near the center of a bright galaxy, within a stellar halo or stellar diffraction spike. Some of these objects are not detected (for instance, because the entire

region is masked), and some are detected but the GalFit fit fails to converge. Luckily, these objects can be (and are, see Section 3.4) identified based on a visual inspection.

The second point is further explored in Figures 20(a)–(e), which show the recovery rate (fraction of detected to input galaxies) in a two-dimensional space defined by the input galaxy magnitude, *m*, and, in turn, *n*, $\mu_0$, $\mu_e$, $\langle \mu_e \rangle$, and $r_e$. At any given magnitude, the recovery rate does not appreciably depend on the Sérsic index *n*—that is, galaxies with *n* in the entire range explored by the simulations have roughly the same probability of being detected, with this probability decreasing as the galaxies become fainter. The situation is markedly different in terms of surface brightness: at any given magnitude, the probability of detection is a steeply declining function of surface brightness, but this function is largely independent of magnitude, as indicated by the nearly vertical line dividing the gray from the black region in the middle three panels of Figures 20(a)–(e). The behavior in $r_e$ is again different: as a galaxy becomes fainter, it also needs to be progressively smaller to be detected. This can be easily understood because if the critical $\mu_e$ value at which galaxies become undetectable is not a function of *m*, then fainter galaxies must have smaller sizes to maintain $\mu_e$ above the detection limit. More precisely, for a Sérsic model, $r_e$ can be expressed as function of *m*, $\mu_e$, and *n* (see Equations (9) and (10) of Graham & Driver 2005): if the $\mu_e$ value needed for detection is not a function of *m*, while the recovery rate is independent of *n*, then the critical $r_e$ value at which galaxies become undetectable will scale approximately as $10^{-0.4m}$, which is exactly the behavior shown in the figures.

Figures 21(a)–(e) compare recovered and input parameters as a function of input parameters; expanded views, along the ordinate, are shown in Figures 22(a)–(e). Galaxies do cluster along the $\Delta x = 0$ ridgeline (with $x = m$, *n*, $\mu_0$, $\mu_e$, $\langle \mu_e \rangle$, $r_e$), where $\Delta$ measures the difference between input and recovered parameters (normalized to the input values in the case of *n* and $r_e$). As expected, the distributions in surface brightness (and, to a lesser extent, magnitudes) flare for faint, low surface brightness galaxies, a combination of photometric errors becoming more severe and, at the faintest surface brightness limits, of the fact that a galaxy’s surface brightness must be biased high (due to noise or confusion from nearby sources) for that galaxy to be detected at all. Related, although less immediately obvious, is the slight tendency for the distribution in recovered $r_e$ to be skewed toward larger $r_e$ values (bottom panels of Figures 21(a)–(e)). Further inspection shows that galaxies for which $r_e$ is overestimated (beyond what is expected simply due to photometric errors) tend to cluster at input $\mu_e \sim 28$ (in the *g*-band), that is, at about the level at which detection becomes problematic. As noted above, for these galaxies the recovered surface brightness tends to be biased high. Because *n* does not show a bias for these galaxies, overestimating the surface brightness (magnitude) immediately implies that $r_e$ must also be slightly overestimated, as observed.

Finally, no significant biases are seen as a function of projected ellipticities. Figure 23 explores how the ellipticity $\epsilon$ of the input galaxies affects the completeness rate. As shown in Figure 4 of Sánchez-Janssen et al. (2016), ellipticities are recovered within 20% of the input value, with no noticeable bias as a function of the galaxy surface brightness; furthermore, the detection rate of galaxies of all sizes appears to be largely independent of $\epsilon$ (right panel of Figure 23). There is, however,
<figure><img src="image_40.png" /><figcaption>**Figure 19.** (a) Distribution of input (black histogram) and recovered (red histogram) parameters for the 36,500 galaxies injected in the core region frames, with the absolute numbers of objects shown on the ordinate scale to the left. The green circles with error bars show the completeness (number of recovered galaxies divided by the number of input galaxies) as a function of input parameters and measured according to the scale shown on the ordinate to the right. Note that the green points are not obtained by dividing the red by the black histogram, because in the presence of photometric errors and biases the recovered value of any given parameter might not be in the same bin as the input value for the same galaxy. The panels show (left to right, top to bottom) $u^*$-band magnitude (the absolute magnitude scale is shown in the bottom abscissa, while the top abscissa shows the apparent magnitude scale), Sérsic index, central surface brightness, surface brightness measured at the effective radius, surface brightness averaged within one effective radius, and effective radius (given in parsecs on the bottom axis and in arcseconds on the top axis). Note that while magnitude, Sérsic index, and effective radius are input to the models, the surface brightness parameters are derived quantities, uniquely defined by *n*, *M*, and *r*<sub>e</sub> for a Sérsic profile. Magnitudes and surface brightnesses are as measured, i.e., not corrected for Galactic extinction. (b) Same as Figure 19(a), but in the *g*-band. (c) Same as Figure 19(a), but in the *r*-band. (d) Same as Figure 19(a), but in the *i*-band. (e) Same as Figure 19(a), but in the *z*-band.</figcaption></figure>
<figure><img src="image_41.png" /><figcaption>Figure 19. (Continued.)</figcaption></figure>
<figure><img src="image_42.png" /><figcaption>Figure 19. (Continued.)</figcaption></figure>

a trend in the recovery rate as a function of $\epsilon$ for the faintest and lowest surface brightness galaxies (left and central panels of Figure 23): at $m \gtrsim -9$ mag and $\mu_e \gtrsim 28 \text{ mag arcsec}^{-2}$ the recovery rate decreases slightly as the galaxies project to a rounder shape ($\epsilon \to 0$). This is due to the fact that at any given total magnitude, $m$, the effective surface brightness of a galaxy with a given intrinsic axial ratio is lower when the galaxy is seen face on, with the result that at low ellipticities, galaxies are more easily pushed beyond the surface brightness threshold at which the detection rate drops dramatically.

In conclusion, our extensive simulations confirm the robustness of our detection algorithm and allow us to firmly characterize and account for incompletenesses and biases in our upcoming studies of the photometric and structural parameters of Virgo galaxies, including investigations of the luminosity function and structural scaling relations.

## 5. Derivation of Structural Parameters

The GalFit fits described in Section 3.3 provide global structural parameters—magnitudes, effective radii, ellipticities, major axis position angles. However, for some galaxies, GalFit fails to converge; additionally, in the VCands implementation, GalFit does not allow for radial changes in ellipticity and position angles, and only very rough criteria are applied in deciding whether a galaxy hosts a separate nuclear component.

For these reasons, we rederive accurate structural parameters (total magnitude, effective radius, concentration, central surface brightness, and surface brightness at, and averaged within, one

effective radius, as well as ellipticity, major axis position angle, and deviations of the isophotes from pure ellipses) for each of the 404 bona fide Virgo members in the core region using three independent methods: parametric fits to the surface brightness profile, derived from a full isophotal analysis of the images; a nonparametric curve-of-growth analysis; and (for galaxies fainter than $m_g = 13$ mag) one- or two-component two-dimensional fits to the light distribution.

### 5.1. Isophotal Analysis and Parametric Fits to the Surface Brightness Profiles

A full isophotal analysis was performed for all bona fide Virgo cluster members in the core region. Within our team, the code that performs this task is affectionately known as Typhon: in Greek mythology, Typhon was the “father of all monsters, a fire-breathing dragon who had one hundred heads that never slept.”<fnref n="39" /> Typhon is a Python interface incorporating a variety of external codes, including IRAF tasks, JAVA scripts, and Perl and Fortran programs, as well as calls to standard packages, such as SExtractor. Typhon is largely automated but, as explained in more detail below, is followed by a thorough visual inspection and assessment of the results, so that steps deemed not to have been performed correctly are carried out again interactively. For each galaxy, Typhon comprises the following steps:

1. Extraction of image cutouts (in each filter) and setup of the parameters required by the steps to follow;

<footnote n="39">³⁹ http://www.greekmythology.com/Other_Gods/Typhoeus/typhoeus.html</footnote>
<figure><img src="image_43.png" /><figcaption>**Figure 20.** (a) Hess diagram showing the recovery fraction for the 36,500 simulated galaxies injected in the core region frames, from 0% (black) to 100% (white, as indicated by the gray scale above the plot). From left to right, the panels show, as a function of magnitude (absolute on the left-hand axis and apparent on the right-hand axis) Sérsic index, central surface brightness, surface brightness measured at the effective radius, surface brightness averaged within one effective radius, and effective radius (in parsecs). The solid lines represent the scaling relations best fitting a combination of known Virgo galaxies and Local Group galaxies, with 3σ scatter shown by the red dashed lines. Magnitudes and surface brightnesses are as measured, i.e., not corrected for Galactic extinction. (b) Same as Figure 20(a), but in the g-band. (c) Same as Figure 20(a), but in the r-band. (d) Same as Figure 20(a), but in the i-band. (e) Same as Figure 20(a), but in the z-band.</figcaption></figure>
<figure><img src="image_44.png" /></figure>

<figure><img src="image_45.png" /><figcaption>Figure 20. (Continued.)</figcaption></figure>
<figure><img src="image_46.png" /><figcaption>Figure 20. (Continued.)</figcaption></figure>

2. Creation of a mask identifying foreground/background contaminants as well as artifacts;

3. Isophotal fitting and extraction of one-dimensional profiles for surface brightness, ellipticity, major axis position angle, isophotal center, and deviations of the isophotes from pure ellipses;

4. Nonparametric curve-of-growth analysis and determination of the background;

5. Parametric fits to the surface brightness profiles.

All steps are described in more detail below.

### 5.1.1. Steps 1 and 2: Setting up the Code and Creation of the Mask

Step 1 is a preparatory step that consists of visually inspecting images centered on each galaxy, determining the size of the cutouts for further analysis, and estimating the galaxy center, ellipticity, and major axis position angle to be used as initial guesses for steps 2 and 3. The size of the cutout is chosen to extend beyond the visible boundary of the galaxy —typically over 20 effective radii—but is not arbitrarily large, both to limit processing time and to avoid as much as possible complications arising from a varying background or nearby objects.

Masking contaminants (including artifacts, foreground stars, stellar halos—unless the target galaxy is completely embedded in one—background galaxies, as well as globular clusters) is necessary to aid the isophotal fitting carried out in the next step. The procedure needs to be adjusted according to the type of

galaxy being processed. For instance, in the case of a star-forming galaxy, it is important to avoid masking H II regions. Furthermore, the efficiency of any source detection algorithm will depend on the underlying background level, with the result that any such algorithm will miss an increasingly larger fraction of contaminants as one approaches the center of the target galaxy, as the underlying surface brightness increases. To address these challenges, we adopted an iterative procedure consisting of the following steps:

(a) A first *SExtractor* run is carried out with a low $\sigma$ threshold (i.e., designed to detect objects as faint as possible), but limiting the amount of deblending (or, in *SExtractor* parlance, segmentation).

(b) Since the procedure above might detect (and therefore mask) the target galaxy, all objects in a 20 × 20 pixel box around the galaxy center are identified in *SExtractor's* segmentation image and removed from *SExtractor's* object image, which is then fed as a mask to IRAF's task *ELLIPSE*, described in more detail in Section 5.1.2.

(c) The output from *ELLIPSE* is splined, and the result is used to create a galaxy model. A median sky, determined from all unmasked pixels outside the elliptical annulus defined by the last fitted isophote, is subtracted from the model, and a residual image is produced.

(d) *SExtractor* is run again, this time on the residual image, with a low $\sigma$ threshold and high deblending, using as weight the original weight image (see Section 3.2).
<figure><img src="image_47.png" /><figcaption>**Figure 21.** (a) Comparison of recovered vs. input parameters for the 36,500 simulated galaxies injected in the *u*-band core region images (fields NGVS+0+0, NGVS+0+1, NGVS-1+0, and NGVS-1+1). The panels show the difference between input and recovered parameters plotted against input parameter, for (from top to bottom) magnitude (the absolute magnitude scale is shown in the bottom abscissa, while the top abscissa shows the apparent magnitude scale), Sérsic index, central surface brightness, surface brightness measured at the effective radius, surface brightness averaged within one effective radius, and effective radius. In the case of the effective radius and Sérsic index, the difference between input and recovered parameters is normalized to the input value. The contours are drawn logarithmically for point surface densities between 2 and 200 (e.g., 2, 6.3, 20, 63.2, 200), where the surface density is calculated in regions whose sizes are shown by the gray boxes on the top left of each panel (see Figure 22(a) for an expanded view). Note that only the Sérsic index, surface brightness at the effective radius, and effective radius are actual inputs describing the structure of the simulated galaxies, while central surface brightness and surface brightness averaged within one effective radius are derived parameters. See text for further details. (b) Same as Figure 21(a), but in the *g*-band. (c) Same as Figure 21(a), but in the *r*-band. (d) Same as Figure 21(a), but in the *i*-band. (e) Same as Figure 21(a), but in the *z*-band.</figcaption></figure>
<figure><img src="image_48.png" /><figcaption>Figure 21. (Continued.)</figcaption></figure>

multiplied by the background-subtracted and scaled galaxy model. The goal of this step is to detect faint objects as close as possible to the center of the galaxy, while avoiding detecting the actual target galaxy. The weight image is designed to prevent SExtractor from detecting high S/N areas and artifacts in the residual image resulting from subtraction of an imperfect isophotal model.

(e) The final mask is created: outside an ellipse with semimajor axis larger than one-third of the image size we adopt the mask produced in step (b),<fnref n="40" /> while within this ellipse, we adopt the mask created from step (d). The mask is then blurred with a circular Gaussian with $\sigma$ equal to 0.6 pixels, so as to include in the mask low surface brightness extensions of masked objects. Finally, bright stars identified using a combination of the automask task in the THELI data-reduction package (Erben et al. 2005, 2009) and customized software that masks CCD bleed trails (see NGVS-I) are added to the mask.

The procedure is tweaked slightly according to the type of galaxy being processed. Most notably, star-forming and spiral galaxies are flagged during the preparatory step; in these cases, the scaling factor used in the weight image is set lower and the $\sigma$ threshold in the second SExtractor run is set higher than

in the case of a galaxy with a smooth surface brightness distribution, forcing SExtractor to only detect the brightest objects. This proves effective in leaving H II regions unmasked.

We note that the masking procedure described above is different from the one discussed in Section 3.2, the latter relying on a combination of SExtractor plus THELI/ automask. The reason why the procedure adopted by Typhon could not be implemented in VCands is that step (c) above relies on feeding ELLIPSE reasonably accurate initial guesses for the galaxy center, ellipticity, position angle, and fitting starting radius that are best set interactively (as in step 1 above). This would not be feasible at the detection stage, where over 1 million galaxies are being processed. Additionally, ELLIPSE is more prone to convergence failures than GalFit and therefore not as suited for a fully automated code. Conversely, the masks created by VCands are not ideal for use in Typhon, as they often are overly conservative in masking objects. This is not an issue when running GalFit, but it is when running ELLIPSE, whose convergence relies on a smaller number of fitted data points (those within the annulus being fitted).

### 5.1.2. Step 3: Isophotal Fitting

Isophotes are fitted using the ELLIPSE task in IRAF. ELLIPSE follows the methodology described in Jedrzejewski (1987) and Peletier et al. (1990): for each semimajor axis length, the intensity, $I(\Phi)$, is azimuthally sampled in a number (generally between 30 and 120) of sectors (of approximately constant area) within an elliptical annulus described by an initial guess for the isophote's center (X, Y), ellipticity ($\epsilon$), and semimajor axis position angle ($\theta$), with width increasing logarithmically as a function of semimajor axis length. $I(\Phi)$, which is taken as the mean of all unmasked pixels within each sector, is expanded into a Fourier series as

$$I(\Phi) = I_0 + \sum_{k=1}^{4} [A_k \sin(k\Phi) + B_k \cos(k\Phi)]. \quad (7)$$

The best-fitting set of parameters X, Y, $\epsilon$, and $\theta$ are those that minimize the sum of the squares of the residuals between the data and the ellipse when the expansion is truncated to the first two moments ($k=1, 2$, which completely describe an ellipse). Higher order moments ($k=3, 4$) define deviations of the isophotes from ellipses. The third-order moments (A3 and B3) represent isophotes with three-fold deviations (e.g., egg shaped or heart shaped), while the fourth-order moments (A4 and B4) represent four-fold deviations. Rhomboidal or diamond-shaped isophotes translate into a nonzero A4. For galaxies that are not distorted by interactions, B4 is the most meaningful moment: a positive B4 indicates “disky” isophotes (i.e., with semimajor axis $B4 \times 100\%$ longer than that of the best-fitting ellipse), while a negative B4 indicates “boxy” isophotes (i.e., with semimajor axis $B4 \times 100\%$ shorter than that of the best-fitting ellipse; Jedrzejewski 1987).

During the isophotal fitting, the semimajor axis was increased logarithmically, with each isophote calculated at a semimajor axis 10% longer than that of the isophote preceding it, except for the case of very low surface brightness galaxies, for which a longer step, 20%, was adopted to increase the S/N within the fitting annuli. During the automated phase, all parameters were allowed to vary freely, although after visual inspection, it was sometimes found necessary to repeat the process while fixing one or more of the parameters (see below).

<footnote n="40">⁴⁰ The cutout is selected so that beyond this radius, the contribution from the galaxy itself is negligible, and therefore subtraction of the galaxy model is not just unnecessary but in fact undesirable as it might introduce spurious features in the residuals.</footnote>
<figure><img src="image_49.png" /><figcaption>**Figure 22.** (a) Same as Figure 21(a), but showing an expanded view along the ordinate. (b) Same as Figure 21(b), but showing an expanded view along the ordinate. (c) Same as Figure 21(c), but showing an expanded view along the ordinate. (d) Same as Figure 21(d), but showing an expanded view along the ordinate. (e) Same as Figure 21(e), but showing an expanded view along the ordinate.</figcaption></figure>
<figure><img src="image_50.png" /><figcaption>Figure 22. (Continued.)</figcaption></figure>
<figure><img src="image_51.png" /><figcaption>Figure 22. (Continued.)</figcaption></figure>

All fits were terminated when the semimajor axis reached half the size of the cutout (which was chosen to extend significantly beyond the visual extent of the galaxy). In practice, ELLIPSE fails to converge before reaching this limit, usually because the small radial gradient in the surface brightness profile that characterizes the outer regions prevents convergence from being reached. When this happens, the surface brightness profile at larger radii is recovered by running ELLIPSE with $ϵ$, $θ$, and the isophotal center fixed to the mean values calculated for the outermost five fitted isophotes, generally spanning a factor $1.1^4 = 1.46$ in semimajor axis length.

As part of the isophotal fitting process, the best-fitting parameters are used to generate a galaxy model, which, once added to an estimate of the sky, is subtracted from the original image to obtain a residual image.

### 5.1.3. Step 4: Curve of Growth and Estimate of the Background

Curve-of-growth parameters and a background estimate are obtained in a two-step iterative process that involves a parametric fit to the surface brightness profile described in step 5.

In the first iteration, the mode of the counts from all nonmasked pixels beyond the last fitted isophotes is used as a background estimate. This is often a good approximation of the true background value but hinges on the assumption that, for each galaxy, the last fitted isophotes (which always have a semimajor axis equal to half the size of the cutout) include all of the galaxy flux. To improve upon this assumption, the mode estimate of the background is subtracted from the surface

brightness profile determined during step 3 and a parametric fit to the profile is performed as described in step 5. The fit produces, among other things, an estimate of the galaxy effective radius, $r_e$, and this is then used to refine the region within which the background should be measured.

To do so, a curve of growth is produced for each galaxy. Total fluxes are measured in an image obtained by substituting, in the original galaxy image, all masked objects (as identified in step 2) with the corresponding values in the galaxy model (obtained as part of the isophotal analysis described in step 3). This can of course only be accomplished in the area covered by the model (i.e., within an ellipse with semimajor axis equal to half the size of the image); outside this area, masked pixels are substituted with the background value estimated by SEx-tractor during step 1. Cumulative, enclosed fluxes are then calculated within each best-fitting elliptical isophote determined during step 3. For galaxies described by a Sérsic profile, the radius $r_{0.01}$ within which the enclosed magnitude is within 1% of the total magnitude (extrapolated to infinity) depends on the Sérsic index $n$ (see Graham & Driver 2005): for instance, for $n = 0.5$, $r_{0.01}/r_e = 2.7$, that is, the flux within 2.7 effective radii is within 0.01 mag of the total flux; $r_{0.01}/r_e$ increases with $n$, and at $n = 4$ (i.e., a de Vaucouleurs profile), $r_{0.01}/r_e = 19.7$. For most low-mass galaxies, $n$ is in the range 0.5–2, corresponding to $r_{0.01}/r_e \sim 2.7–7.7$. An improved background estimate is then obtained as the value giving the flattest curve of growth between $r_{0.01}/r_e$ and $1.5 \times r_{0.01}/r_e$. The background thus determined is compared to the mode determined as described above, and the galaxy is flagged for further analysis
<figure><img src="image_52.png" /><figcaption>Figure 23. Completeness rate (ratio between the number of recovered, $x$, to the number of input, $N$, galaxies) as a function of the ellipticity of the input galaxy. From left to right, the panels show galaxies binned in magnitude, surface brightness at the effective radius, and effective radius, as shown in the legend. All parameters are measured in the g-band. The errors on the completeness correspond to the binomial confidence interval and are equal to $\sqrt{x/N \times (1 - x/N)/(N + 1)}$.</figcaption></figure>

if the two values differ by more than 10% (these galaxies are then processed interactively to determine the best background value).

The background estimate thus obtained is subtracted from the curve-of-growth fluxes as well as from the surface brightness profile. A total curve-of-growth magnitude is estimated as the (background-subtracted) mean of the fluxes enclosed within isophotes with a semimajor axis between $r_{0.01}/r_e$ and $1.5 \times r_{0.01}/r_e$; the effective radius (defined as the radius including half the total curve-of-growth magnitude), concentration (defined as the ratio of the radii including 80% and 20% of the total flux), as well as the surface brightness at, and averaged within, one effective radius are then measured nonparametrically directly from the images. As a sanity check, the effective radius determined from the curve-of-growth analysis is compared to that derived from the parametric fit to ensure consistency. Finally, the background-subtracted surface brightness profile is fitted using the parametric models described in step 5.

### 5.1.4. Step 5: Parametric Fits to the Profile

Surface brightness profiles of all galaxies were fitted using a Sérsic (1968) and a double-Sérsic profile. The radial

dependence of the flux for a Sérsic (1968) profile is described as

$$I(r) = I_e \exp \left\{ -b_n \left[ \left( \frac{r}{r_e} \right)^{1/n} - 1 \right] \right\}, \quad (8)$$

where $b_n \approx 1.992n-0.3271$ (e.g., Caon et al. 1993; Graham & Driver 2005) and $n$ controls the overall shape of the profile, with low $n$ values producing curved profiles with logarithmic slopes that are shallow in the inner regions and steep in the outer parts, while high $n$ values produce extended profiles with less overall curvature. For $n=1$, a Sérsic model becomes a pure exponential, while for $n=4$ it reduces to a classical de Vaucouleurs profile. To account for the (possible) presence of a stellar nucleus, double-Sérsic profiles composed of an outer (describing the main body of the galaxy) and an inner (describing the nucleus) Sérsic profile are also fitted to each galaxy; in these cases, the Sérsic index for the nuclear component was fixed to $n=2$, as this value is roughly the mean value derived by fitting the observed surface brightness profile of Galactic globular clusters (P. Côté 2019, private communication). The number of free parameters in a Sérsic
<figure><img src="image_53.png" /><figcaption>**Figure 24.** Main products of the isophotal fitting analysis, performed by *Typhon*, and shown here for VCC 1407 (NGVS J12:32:02.74+11:53:24.3, $m_g = 14.77$ mag uncorrected for Galactic extinction). The top row shows composite *u**, *g*, *i* color images, on two different spatial scales and contrast. The middle row shows, from left to right, a full cutout of the galaxy, 4'67 across; the final mask; the ellipse model; the residual obtained by subtracting the model (from which the best estimate of the sky has been subtracted) from the original image; and the image used for the curve-of-growth analysis (all in the *g*-band). Note that the ellipse model does not, by design, extend to cover the full cutout; the lack of a discontinuity in the residual image marking the location of the largest isophote is an indication that the sky has been estimated correctly. The bottom row shows a zoomed-in version of the middle row, displaying a region 34" on the side. Note that while all contaminants (best seen in the residual image, most of them globular clusters associated with the galaxy itself) are successfully accounted for in the mask image, the nucleus remains unmasked. The ellipse model is extremely successful in reproducing the galaxy, as shown by the lack of residual flux at any radius, including at the nuclear location. See Section 5.1 for details.</figcaption></figure>

profile is three ($I_e$, *n* and $r_e$), while the number of free parameters in a double-Sérsic profile is five.

Note that the brightest galaxies (e.g., M87) have low-density cores with surface brightness profiles that fall below the inward extrapolation of the Sérsic model best characterizing the main galaxy body (e.g., Côté et al. 2006, 2007; Ferrarese et al. 2006) and are best described by “core-Sérsic” profiles (Trujillo et al. 2004, see also Graham et al. 2003). Since only a small percentage of galaxies require core-Sérsic fits, these are done on a case-by-case basis and are not performed for all galaxies.

All minimizations were carried out using the *Minuit* package in CERN's program library using a Simplex minimization algorithm (Nelder & Mead 1965) whose minima are refined using an inexact line search (MIGRAD, see Ferrarese et al. 2006 for further details). Before being compared to the observed profile, the models are convolved with the one-dimensional,

azimuthally average surface brightness profile of the MegaCam PSF. In the fitting part of *Typhon*, the surface brightness is a function of the “geometric mean radius” defined as $r_{geo} = a\sqrt{1 - \epsilon(a)}$, where *a* is the semimajor axis length and $\epsilon$ is the ellipticity measured as a function of *a*. The fits are performed for $r_{geo}$ ranging from 0.187 (i.e., 1 pixel) to the radius at which the surface brightness reaches the limits listed in Table 2, and all points in the profile are weighted according to the formal errors returned by the isophotal fitting procedure.

### 5.1.5. Special Cases and Visual Checks

Some galaxies require special attention before they can be processed through *Typhon*:

1. Galaxies that fall close to field boundaries should not, ideally, have cutouts extracted from the original stacks,
<figure><img src="image_54.png" /><figcaption>**Figure 25.** The top two rows show the full (4!67 across) cutouts (top) and residuals (bottom) for VCC 1407, in the (from left to right) *u*'-, *g*'-, *r*'-, *i*'-, and *z*- bands. A zoomed-in version, 34'' on a side, is shown in the bottom two rows. In both the top and bottom rows, the surface brightness scale refers to the *g*-band image; the other bands are shifted relative to *g* by +0.5, -0.5, -1.0, and -1.5 mag for *u*', *r*, *i*, and *z*, respectively. Note that some residual fringing is present in the *z*-band.</figcaption></figure>

both because the S/N is lower near the fields' edges and because the galaxy itself might extend beyond the edge of the stack on which its center is located. A clear example is M87 itself: although the galaxy center is located in field NGVS+0+0, its halo extends to all three neighboring core region fields. For these galaxies, adjacent fields are mosaiced using the SWarp software (Bertin et al. 2002) and cutouts—to be fed to Typhon—are then extracted from the “swarped” images.

2. The light distribution of some galaxies is severely affected by contamination from nearby comparably bright or brighter galaxies. An example is VCC 1297 (NGC 4486B), which, projecting only 7.3 from the center of M87, is deeply embedded in the bright and spatially varying halo of Virgo's cD. For these galaxies, a model of the brighter companion is subtracted before the galaxy itself is processed. In the case of galaxies of similar brightness, Typhon is run iteratively on each galaxy,

each time subtracting the best model of the companion, until stable results are achieved.

3. The centers of the brightest galaxies in Virgo are saturated in the NGVS long exposures: throughout the cluster, 105 galaxies have centers that saturate in the *i*-band (11 in the core region); of these, 3, 99, and 85 also saturate in the *u*'-, *g*'-, and *z*-bands, respectively. In a couple of cases, the galaxy itself is not saturated but is crossed by the diffraction spike of a nearby, saturated foreground star. In all of these cases, the saturated areas are replaced with the (appropriately aligned and scaled) corresponding regions extracted from the NGVS short exposures. No attempt is made to match the PSF of the long and short exposures: the saturated area always extends to several PSF FWHM, making an exact PSF match unnecessary. When fitting the surface brightness profile of galaxies whose center was corrected for saturation, Typhon uses the PSF appropriate for the short exposure stack.
<figure><img src="image_55.png" /></figure>

**Figure 26.** Data products from Typhon's isophotal analysis, shown here for the g-band image of VCC 1407 (see Figures 24 and 25). The top two panels show the surface brightness profile (left) and curve of growth (right); the black, red, and cyan points use a mean, midpoint, and mode estimate of the background, measured using all unmasked pixels within the cutout and beyond the isophote with the largest radius. The green points use an optimal estimate of the background obtained by requiring a flat curve of growth at large radii (see Section 5.1.3 for details). Note that the different background estimates only affect the surface brightness profile below 29 mag arcsec⁻², and, as a consequence, the curve of growth is largely insensitive. The magenta line in the left panel represents the surface brightness profile measured from the HST ACS/F475W images taken as part of the ACSVCS (Ferrarese et al. 2006), transformed to the SDSS system as described in Chen et al. (2010). The two vertical green lines in the curve-of-growth profile indicate the region within which the curve-of-growth magnitude is measured. The other panels show ellipticity *ϵ* = 1 - *b*/*a*, with *a* and *b* equal to the major and minor axis, respectively, the major axis position angle (measured from north to east), the B4 coefficient, indicating fourth-order deviations of the isophotes from ellipses, and the position of the center relative to the average isophotal center. The magenta dots represent the same quantities measured from ACSVCS images (Ferrarese et al. 2006). All quantities are plotted as a function of the geometric radius *r*<sub>geo</sub> = *r* × √(1 - *ϵ*), where *r* is the semimajor axis.

4. In the specific case of galaxies in the four core region frames, the surface brightness at radii larger than a few arcminutes can be biased when using the global background stacks, with the amount of such bias increasing (in a not easily quantifiable way) at larger scales and fainter surface brightness (see NGVS-I for details). In these cases, Typhon was run twice, first on the global background stacks and then on the (lower resolution, see Table 3) Elixir-LSB stacks. The profiles for all isophotal parameters are then a hybrid between those obtained from the global (in the inner region) and the Elixir-LSB (in the outer region) stacks, with the exact radius where the transition occurs determined on a case-by-case basis to ensure that the profiles are not sensitive to differences in the PSF. The background value is measured from the Elixir-LSB stacks and applied to the entire, hybrid surface brightness profile and curve of growth.

After Typhon is run in an automated fashion, all results (mask image; outputs from the isophotal fitting, including model and residual images; curve-of-growth analysis; and parametric fits to the surface brightness profiles) are visually inspected in each band. Steps that were not performed correctly are repeated interactively. The most common occurrences are failure of ELLIPSE to converge and/or an incorrect estimate of the background resulting from improperly masked nearby contaminants (mostly bright stellar haloes). About 25% of the galaxies need to have one or more steps repeated, in one or more filters. During the visual inspection, galaxies requiring core-Sérsic fits to the surface brightness profiles are identified and the fits are performed. Finally, each galaxy is assigned a flag according to whether it is judged to be nucleated (1) or nonnucleated (0) or has a nucleus that is offset relative to the isophotal center (2). The judgment is based on the relative quality of the Sérsic and double-Sérsic fits (as measured by the
VCC1407 (= TH74, IC3461)
NGVSJ12:32:02.74+11:53:24.3

<figure><img src="image_56.png" /></figure>

**Figure 27.** Surface brightness profiles (black points with gray error bars) and parametric fits for VCC 1407, plotted as a function of the geometric radius $r_{geom} = r \times \sqrt{1 - \epsilon}$ and using the optimal sky estimate (green points in the top left panel of Figure 26). The profiles are only plotted to the 2σ surface brightness limit of the data (Table 2). The red lines represent the best-fitting Sérsic profiles, while the solid green line represents the best-fitting double Sérsic profile, with inner (nuclear) and outer (main body of the galaxy) components shown as the dotted and dashed green lines, respectively. The dashed blue line represents the PSF profile, as determined at the nuclear location; the PSF FWHM is indicated in each panel. Finally, the magenta lines superimposed to the g- and z-band data represent the best-fitting King+Sérsic profiles determined from the ACS/F475W and F850LP ACSVCS data (Ferrarese et al. 2006), transformed to the SDSS system as described in Chen et al. (2010).

fit $\chi^2$), as well as visual inspection of the images and surface brightness profiles.

The final step in the Typhon processing is designed specifically to measure accurate colors. For each galaxy, Typhon is run independently in each filter. This is appropriate when trying to bring out wavelength-dependent changes in structural parameters. However, when measuring colors, identical masks and apertures need to be adopted in every filter for consistency. Once the g-band Typhon solution was validated for each galaxy, a “master mask” was created including all pixels masked in any band, and Typhon was run one more time on the $u^*$-, $g$-, $r$-, $i$-, and z-band images, but now fixing the isophotal solution to the one determined in the g-band during the main isophotal run. Integrated colors were then measured directly by integrating the surface brightness profiles from the center out to one effective radius, as measured in the g-band.

5.1.6. *Outputs from the Isophotal Fitting, Curve-of-growth Analysis, and Surface Brightness Profile Parameterization*

Figures 24–27 show the most relevant outputs produced by Typhon in the case of a specific Virgo member, VCC 1407 (IC 3461), a regular, fairly bright ($m_g = 14.8$ mag) early-type galaxy, classified in the VCC as a nucleated dwarf Elliptical (dE). The top two panels of Figure 24 show, in two different spatial scales, a composite $u^*gi$ color image centered on the galaxy; the panel to the right (and all other panels in this and the next figure) corresponds to the cutout fed to Typhon, in this case of side equal to 4'67. This can be compared to $r_{0.01} \sim 1.4'$ derived for the main body of the galaxy, which is well fitted by a Sérsic model with $r_e = 11.3'$ and $n = 1.5$. The panels in the middle row show, from left to right, the g-band image for the full cutout, the mask (step 2), the model and residual images (step 3), and the image from which the curve of growth is measured (step 4). The same images, but zoomed in
by a factor of ~8 and with a different gray scale to bring out the nucleus, are shown in the bottom row. It is noteworthy that *Typhon* could correctly identify and mask contaminants all the way to the center of the galaxy, while not masking the nucleus itself, even though these contaminants, while clearly visible in the residual image, are only marginally detectable in the original image. Also noteworthy is the fact that there is no indication, in the residual image, that the sky might not have been estimated correctly: the residual image is produced by subtracting the model (third panel from the left), to which the sky (measured as described in Section 5.1.3) is added, from the original image (first panel from the left). An incorrectly determined sky would thus translate into a visible “step” in the residual image along the ellipse defined by the largest isophote. The original (top) and residual (bottom) images in all bands (*u**, *g*, *r*, *i*, *z* from left to right) are shown in Figure 25, with the bottom two rows showing a zoomed-in view of the nuclear region.

Figure 26 shows the results of the isophotal fitting (Section 5.1.2 we show here the results for the g-band, but similar plots are produced by Typhon for all other bands). The top two panels show the surface brightness profile (left) and the curve of growth (right), plotted as a function of the geometric mean radius $r_{geo}$. The black, red, and cyan points show the profiles and curve of growth assuming a background equal to the mean, midpoint, and mode, respectively, of all unmasked pixels beyond the last fitted isophote (Section 5.1.3). The points essentially overlap with each other in the curve-of-growth profile, while in the surface brightness profile, the cyan points are barely visible as they overlap with the green points (and associated gray error bars). The latter are obtained using the “best” estimate of the background described in Section 5.1.3. The remaining panels show the radial profile of the ellipticity $\epsilon$, major axis position angle $\theta$ (measured in degrees from north to east), B4 Fourier coefficient measuring fourth-order deviations of the isophotes from pure ellipses (see Equation (1)), and location of the center relative to the average (within one effective radius) center of the isophotes, all plotted as a function of $r_{geo}$ up to the surface brightness limits defined in Table 2. The magenta line overplotted on the surface brightness profiles and the magenta points on the ellipticity, position angle, and B4 profiles show the parameters determined from the F475W Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) images of the same galaxy published by Ferrarese et al. (2006) as part of the ACS Virgo Cluster Survey (ACSVCS). The agreement between the HST and MegaCam parameters is excellent except in the inner ~1", where the superior resolution of HST results in a sharper surface brightness profile.

Finally, Figure 27 shows parametric fits to the surface brightness profiles in each bands, as indicated in the bottom left corner of each panel. The blue dashed lines show the azimuthally averaged profile of the PSF determined at the location of the nucleus (the PSF FWHM is listed at the bottom left corner of each panel). The red solid lines show the best-fitting Sérsic models that, in this case, are inadequate given the nucleated nature of the galaxy. The green solid curves represent the best-fitting double-Sérsic models, with individual components shown by the green dotted (nucleus) and dashed (main body of the galaxy) lines. Note that in all filters, the double-Sérsic models slightly underestimate the galaxy flux at the largest radii; this is not an uncommon occurrence, and possible

causes will be discussed in a future paper. The magenta lines superimposed on the g- and z-band profiles represent the HST/ACS F475WE and F850LP profiles determined by Ferrarese et al. (2006), again showing good agreement with the profiles fitted to the MegaCam images.

*Typhon* photometric and structural parameters for all 404 bona fide Virgo members are presented in Tables 4–7.<fnref n="41" /> Specifically, Table 4 lists the J2000 R.A. and decl. (in both degrees and hms/dms) for each target, calculated as the mean position of the isophotal center within one effective radius. The coordinates are used to assign a unique ID to the galaxy (first column), according to IAU standards. The table also lists the membership class (0, 1, or 2 for *certain*, *likely*, and *possible* members, respectively), the ID from the VCC for the galaxies identified there (the cross correlation between our catalog and other surveys is given in Appendix A), the systemic velocity (drawn from a variety of sources, including our own spectroscopic follow-up programs, as referenced in the table), the Galactic reddening (calculated at the location of the galaxy center following Schlegel et al. 1998), the FWHM of the PSF in the NGVS g-band images at the location of the center of the galaxy, and the detection ID, defined as 0 for galaxies detected and fitted by VCands, 1 for galaxies detected by VCands but for which the fit failed, and 2 for galaxies recovered by eye but not detected by VCands (see Section 3).

The results from Typhon’s curve-of-growth analysis and parametric fits to the surface brightness profiles are listed in Table 5. For each method, we give total magnitude (uncorrected for Galactic extinction), $m_g$, effective radius, $r_e$, and surface brightnesses measured at, and averaged within, one effective radius, $\mu_e$ and $\langle\mu_e\rangle$. For the curve-of-growth analysis, we also list the concentration $C_{80/20}$, defined as the ratio between the radii containing 80% and 20% of the total light. For the parametric fits, we give the Sérsic index $n$. Nonnucleated galaxies are identified as “0” under the “Nucleus ID” column, while nucleated galaxies are identified as “1” or “2,” according to whether the nucleus is located at the center of the isophotes (1) or offset from it by more than the PSF FWHM (2). For nucleated galaxies, the Sérsic index refers to the model best fitting the main body of the galaxy, but $m_g$, $r_e$, $\mu_e$, and $\langle\mu_e\rangle$ account for both components. Finally, the table lists the magnitude of the nucleus (uncorrected for Galactic extinction) when it can be reliably derived from the parametric fits. All parameters listed are measured from the g-band images.

Table 6 presents Typhon g-band structural parameters, averaged between 1" and one effective radius (to avoid both including a stellar nucleus, when present, and the smearing effects of the PSF). The uncertainties associated with the ellipticity $\epsilon$, position angle $\theta$ (measured from north to east), and B4 coefficient are the standard deviations in the mean; if the parameter was held fixed while fitting the isophotes, no uncertainty is given. Note that the B4 coefficient is given as a percentage. The table also lists the ellipticity and position angle returned by GalFit (see Section 5.2). Since GalFit does not allow for radial variations in either parameter, the values are those best describing the overall luminosity distribution.

<footnote n="41">⁴¹ We only present global, integrated parameters in this paper; the full results of the isophotal fitting analysis (surface brightness profiles, etc.) will be presented in a future contribution that will include, besides all galaxies in the Virgo core, a magnitude-limited sample of VCC galaxies across the entire NGVS area.</footnote>
Finally, Typhon colors (uncorrected for Galactic extinction) are given in Table 7. The g-band magnitude listed in the table is equal to the value derived using a curve-of-growth analysis and listed in Table 4. The colors are calculated as described at the end of Section 5.1.5 and represent averages between 1" and one effective radius.

## 5.2. Two-dimensional Parametric Fits

Typhon is CPU intensive and requires significant manual intervention. In preparation for the full NGVS catalog covering the entire 104 deg² of the survey, it is thus desirable to identify a reliable but fully automated way of extracting basic photometric and structural parameters for the identified Virgo members, which number in the several thousands. The GalFit procedure included as part of the detection algorithm (VCands, Section 3) has already been proven to be reasonably accurate based on our artificial galaxy simulations (Section 4). To provide consistency with the masking procedure adopted by Typhon, allow for fits to be carried out for galaxies that might have a visual identification but were not be detected (or fitted) by VCands, and provide parameters for a potential nuclear component (masked by VCands), we implemented a new GalFit-based procedure, distinct from the one included in VCands, as follows.

For all galaxies fainter than $g = 13$ mag, GalFit two-dimensional fits to the surface brightness distribution were carried out using a Sérsic fit to represent the main body of the galaxy, plus a PSF to represent the nucleus. If the fitted g-band magnitude of the nucleus was fainter than 26 mag (the $10\sigma$ limit for point-source detection, see Table 2), the fits were repeated using a single Sérsic. GalFit is very sensitive to the initial guesses used for the fit parameters. For the Sérsic component, we used as initial guesses the value of the center, ellipticity, position angle, magnitude, effective radius, and Sérsic index returned by the GalFit run performed by VCands, except for galaxies that were not detected or fitted by VCands, for which the initial value of $n$ was set to 1.0, and the values of the other parameters were as returned by a SExtractor run. For the nuclear PSF, the initial magnitude was set to be 5 mag fainter than the magnitude of the galaxy, as this corresponds to the average galaxy-to-nuclear luminosity ratio (e.g., Côté et al. 2006). All parameters were allowed to vary freely, although the center of the galaxy was constrained to be within 10 pixels (1"/87) of the initial guess. The nucleus was constrained to be centered within 5 pixels of the center of the galaxy and have magnitude between 1 and 10 mag fainter than the main body of the galaxy. Prior to running GalFit, masks were created using the same procedure adopted in Typhon (see Section 5), but using as initial guesses for the galaxy center, ellipticity, and major axis position angle the estimates provided by the GalFit run of VCands (or, when these are not available, an estimate obtained using IRAF's task IMEXAMINE).

A comparison of parameters determined by Typhon and GalFit is discussed in the next section.

## 5.3. Comparison of Structural Parameters Obtained Using Different Methods

The magnitude $m$, surface brightnesses at, and averaged within, the effective radius $\mu_e$ and $\langle\mu_e\rangle$, and the effective radius $r_e$, derived using Typhon parametric fits, curve-of-growth

analysis, and GalFit fits are compared in Figures 28(a)–(e). Figures 29(a)–(e) compare Typhon and GalFit results for the magnitude of the stellar nucleus (if present), the index $n$ of the Sérsic model best fitting the main body of the galaxy, the central surface brightness $\mu_0$, and the mean galaxy ellipticity $\epsilon$. Overall, except for the nuclear magnitudes, there are no biases or scale errors in the parameters recovered by the different methods. With the exception of a few outliers, GalFit performs as well as the curve-of-growth analysis when compared with the parametric fits carried out by Typhon. The GalFit results presented here are fully automated, and no visual checks were performed; upon follow-up, the outliers shown in the figures are easily identifiable with galaxies for which GalFit failed to provide a good model for the data, as judged by the quality of the residuals. Those galaxies can be easily refitted to provide better results.

Sérsic indices, central surface brightnesses, and ellipticities also compare well. Note that GalFit assumes a radially constant ellipticity and position angle, while Typhon allows for radial variation in both (see Section 5.1). In the figures, the Typhon ellipticity values have been averaged between 1" and one effective radius.

The only bias observed is in the nuclear magnitudes recovered by Typhon and GalFit. The latter is effective in identifying stellar nuclei, as demonstrated in Figure 30, which shows the magnitude distribution of all galaxies, as well as nucleated galaxies as identified by the two methods. Note that because our implementation of GalFit constrains the nucleus to be within 5 pixels of the center of the galaxy, and because GalFit will always try to fit a nuclear component to any flux enhancement present in this region, many of GalFit's “nuclei” are spurious detections. The figure shows, however, that galaxies for which GalFit identifies a nucleus within two pixels (0"/37) of the center are mostly also judged to be nucleated based on the (visually aided) Typhon analysis. GalFit, however, recovers nuclei that are systematically fainter, by about 0.1 mag, than those recovered by Typhon. This is a consequence of the fact that the Typhon analysis assumes nuclei described by a Sérsic model with $n = 2$, while GalFit assumes nuclei described by a PSF ($n \sim 0.5$).$^{42}$ In either case, the nucleus is unresolved, but the $n = 2$ model includes additional power at large radii compared with a PSF, leading to slightly brighter total magnitudes. As mentioned in Section 5.1, $n = 2$ is physically justified based on observations of Galactic globular clusters; on the other hand, the NGVS images alone do not allow for a full structural analysis of the nuclei. The measured 0.1 mag difference can therefore be taken as a fundamental uncertainty in the magnitude of the nuclei in the absence of additional information regarding their internal structure.

Note that in all comparisons shown in Figures 28(a)–29(e), the scatter is higher in the $u^*$- and z-bands, as expected because, by design, these bands only reach half depth compared with $g$, $r$, and $i$.

# 6. Conclusions and Summary

We have presented a catalog of 404 bona fide Virgo members, of which 154 are new detections, located within a

<footnote>$^{42}$ We did attempt to run GalFit assuming a Sérsic model for the nucleus, by either fixing $n$ or not. Unfortunately, we found that the fits became quickly unstable, even when the effective radius was constrained to be within very narrow ranges.</footnote>
<table><caption>Table 4
NGVS Virgo Core Region Galaxies: Basic Parameters</caption><thead><tr><th>NGVS ID<br>(1)</th><th>R.A.<br>(deg)<br>(2)</th><th>Decl.<br>(deg)<br>(3)</th><th>R.A.<br>(hms)<br>(4)</th><th>Decl.<br>(dms)<br>(5)</th><th>Class<br>(6)</th><th>VCC ID<br>(7)</th><th>v<br>(km s<sup>-1</sup>)<br>(8)</th><th>δ v<br>(km s<sup>-1</sup>)<br>(9)</th><th>Source<br>(10)</th><th>E(B - V)<br>(mag)<br>(11)</th><th>PSF FWHM<br>(arcsec)<br>(12)</th><th>Det. ID<br>(13)</th></tr></thead><tbody><tr><td>NGVS J12:26:20.07+12:30:37.1</td><td>186.5836092</td><td>12.5103093</td><td>12:26:20.07</td><td>+12:30:37.1</td><td>0</td><td>892</td><td>-690.0</td><td>60.0</td><td>EVCC</td><td>0.033</td><td>0.86</td><td>0</td></tr><tr><td>NGVS J12:26:20.39+12:34:27.3</td><td>186.5849682</td><td>12.5742459</td><td>12:26:20.39</td><td>+12:34:27.3</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.033</td><td>0.83</td><td>0</td></tr><tr><td>NGVS J12:26:22.61+12:47:11.0</td><td>186.5942075</td><td>12.7863945</td><td>12:26:22.61</td><td>+12:47:11.0</td><td>0</td><td>896</td><td>2115.6</td><td>30.0</td><td>EVCC</td><td>0.030</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:26:23.64+13:22:24.7</td><td>186.5984901</td><td>13.3735172</td><td>12:26:23.64</td><td>+13:22:24.7</td><td>0</td><td>898</td><td>...</td><td>...</td><td>...</td><td>0.030</td><td>0.83</td><td>0</td></tr><tr><td>NGVS J12:26:24.04+12:25:00.5</td><td>186.6001506</td><td>12.4168114</td><td>12:26:24.04</td><td>+12:25:00.5</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.83</td><td>0</td></tr><tr><td>NGVS J12:26:26.21+12:39:10.6</td><td>186.6091910</td><td>12.6529437</td><td>12:26:26.21</td><td>+12:39:10.6</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.032</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:26:26.30+11:44:08.0</td><td>186.6096035</td><td>11.7355491</td><td>12:26:26.30</td><td>+11:44:08.0</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.025</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:26:26.97+12:54:23.6</td><td>186.6123749</td><td>12.9065583</td><td>12:26:26.97</td><td>+12:54:23.6</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.80</td><td>2</td></tr><tr><td>NGVS J12:26:27.83+12:45:52.7</td><td>186.6159669</td><td>12.7646250</td><td>12:26:27.83</td><td>+12:45:52.7</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.030</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:26:28.06+12:55:14.2</td><td>186.6168993</td><td>12.9206028</td><td>12:26:28.06</td><td>+12:55:14.2</td><td>0</td><td>903</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.81</td><td>1</td></tr><tr><td>NGVS J12:26:31.31+12:29:32.4</td><td>186.6304526</td><td>12.4923423</td><td>12:26:31.31</td><td>+12:29:32.4</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.032</td><td>0.83</td><td>0</td></tr><tr><td>NGVS J12:26:32.25+12:36:38.5</td><td>186.6343910</td><td>12.6107082</td><td>12:26:32.25</td><td>+12:36:38.5</td><td>0</td><td>912</td><td>90.9</td><td>3.3</td><td>SDSS</td><td>0.032</td><td>0.82</td><td>3</td></tr><tr><td>NGVS J12:26:32.68+13:25:25.8</td><td>186.6361717</td><td>13.4238296</td><td>12:26:32.68</td><td>+13:25:25.8</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.030</td><td>0.83</td><td>0</td></tr><tr><td>NGVS J12:26:33.21+12:44:34.7</td><td>186.6383646</td><td>12.7429799</td><td>12:26:33.21</td><td>+12:44:34.7</td><td>0</td><td>916</td><td>1298.7</td><td>3.3</td><td>SDSS</td><td>0.030</td><td>0.82</td><td>3</td></tr><tr><td>NGVS J12:26:35.84+13:22:44.7</td><td>186.6493325</td><td>13.3790816</td><td>12:26:35.84</td><td>+13:22:44.7</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.028</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:26:36.32+12:48:10.0</td><td>186.6513420</td><td>12.8027898</td><td>12:26:36.32</td><td>+12:48:10.0</td><td>0</td><td>923</td><td>...</td><td>...</td><td>...</td><td>0.030</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:26:37.74+12:43:48.1</td><td>186.6572687</td><td>12.7300152</td><td>12:26:37.74</td><td>+12:43:48.1</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.031</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:26:38.09+11:53:30.7</td><td>186.6587156</td><td>11.8918475</td><td>12:26:38.09</td><td>+11:53:30.7</td><td>0</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.025</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:26:38.25+13:04:44.2</td><td>186.6593632</td><td>13.0789384</td><td>12:26:38.25</td><td>+13:04:44.2</td><td>1</td><td>927</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:26:39.81+12:30:48.8</td><td>186.6658930</td><td>12.5135530</td><td>12:26:39.81</td><td>+12:30:48.8</td><td>0</td><td>928</td><td>-287.7</td><td>6.0</td><td>SDSS</td><td>0.032</td><td>0.83</td><td>0</td></tr><tr><td>NGVS J12:26:41.15+12:50:43.5</td><td>186.6714522</td><td>12.8454060</td><td>12:26:41.15</td><td>+12:50:43.5</td><td>0</td><td>930</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:26:42.11+13:22:33.3</td><td>186.6754391</td><td>13.3759119</td><td>12:26:42.11</td><td>+13:22:33.3</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:26:43.31+12:17:44.0</td><td>186.6804457</td><td>12.2955421</td><td>12:26:43.31</td><td>+12:17:44.0</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:26:44.62+13:11:16.4</td><td>186.6859303</td><td>13.1878925</td><td>12:26:44.62</td><td>+13:11:16.4</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.028</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:26:46.58+13:16:00.6</td><td>186.6940779</td><td>13.2668429</td><td>12:26:46.58</td><td>+13:16:00.6</td><td>0</td><td>937</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:26:46.70+11:41:55.1</td><td>186.6945691</td><td>11.6986515</td><td>12:26:46.70</td><td>+11:41:55.1</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.025</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:26:47.06+12:27:14.3</td><td>186.6961004</td><td>12.4539694</td><td>12:26:47.06</td><td>+12:27:14.3</td><td>0</td><td>940</td><td>1411.5</td><td>9.0</td><td>SDSS</td><td>0.030</td><td>0.83</td><td>3</td></tr><tr><td>NGVS J12:26:47.88+13:22:44.9</td><td>186.6994831</td><td>13.3791465</td><td>12:26:47.88</td><td>+13:22:44.9</td><td>1</td><td>941</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:26:48.25+12:31:35.8</td><td>186.7010531</td><td>12.5266222</td><td>12:26:48.25</td><td>+12:31:35.8</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.032</td><td>0.83</td><td>0</td></tr><tr><td>NGVS J12:26:48.36+13:21:17.7</td><td>186.7015070</td><td>13.3549078</td><td>12:26:48.36</td><td>+13:21:17.7</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:26:48.49+12:23:59.6</td><td>186.7020527</td><td>12.3998780</td><td>12:26:48.49</td><td>+12:23:59.6</td><td>1</td><td>942</td><td>...</td><td>...</td><td>...</td><td>0.028</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:26:49.16+12:18:38.1</td><td>186.7048445</td><td>12.3105772</td><td>12:26:49.16</td><td>+12:18:38.1</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.82</td><td>2</td></tr><tr><td>NGVS J12:26:49.59+12:10:43.0</td><td>186.7066171</td><td>12.1786028</td><td>12:26:49.59</td><td>+12:10:43.0</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:26:50.78+11:33:27.1</td><td>186.7115666</td><td>11.5575223</td><td>12:26:50.78</td><td>+11:33:27.1</td><td>0</td><td>950</td><td>1020.0</td><td>30.0</td><td>EVCC</td><td>0.031</td><td>0.80</td><td>3</td></tr><tr><td>NGVS J12:26:50.83+13:10:36.9</td><td>186.7117767</td><td>13.1769262</td><td>12:26:50.83</td><td>+13:10:36.9</td><td>0</td><td>945</td><td>1.8</td><td>30.0</td><td>EVCC</td><td>0.028</td><td>0.81</td><td>3</td></tr><tr><td>NGVS J12:26:51.99+12:39:08.2</td><td>186.7166382</td><td>12.6522711</td><td>12:26:51.99</td><td>+12:39:08.2</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.031</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:26:54.36+11:39:50.2</td><td>186.7265030</td><td>11.6639359</td><td>12:26:54.36</td><td>+11:39:50.2</td><td>0</td><td>951</td><td>2107.2</td><td>7.2</td><td>SDSS</td><td>0.026</td><td>0.80</td><td>3</td></tr><tr><td>NGVS J12:26:55.15+12:43:13.6</td><td>186.7297719</td><td>12.7204439</td><td>12:26:55.15</td><td>+12:43:13.6</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:26:55.63+12:51:33.6</td><td>186.7317792</td><td>12.8593462</td><td>12:26:55.63</td><td>+12:51:33.6</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:26:55.95+12:59:40.0</td><td>186.7331049</td><td>12.9944579</td><td>12:26:55.95</td><td>+12:59:40.0</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.79</td><td>2</td></tr><tr><td>NGVS J12:26:56.47+12:57:43.3</td><td>186.7352758</td><td>12.9620168</td><td>12:26:56.47</td><td>+12:57:43.3</td><td>0</td><td>956</td><td>2152.5</td><td>30.0</td><td>EVCC</td><td>0.027</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:26:56.67+11:36:12.6</td><td>186.7361079</td><td>11.6035108</td><td>12:26:56.67</td><td>+11:36:12.6</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.028</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:26:57.65+12:25:16.2</td><td>186.7402048</td><td>12.4211559</td><td>12:26:57.65</td><td>+12:25:16.2</td><td>1</td><td>959</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:26:58.93+12:33:13.5</td><td>186.7455459</td><td>12.5537580</td><td>12:26:58.93</td><td>+12:33:13.5</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.030</td><td>0.82</td><td>2</td></tr><tr><td>NGVS J12:26:59.05+12:30:20.5</td><td>186.7460570</td><td>12.5056882</td><td>12:26:59.05</td><td>+12:30:20.5</td><td>0</td><td>962</td><td>...</td><td>...</td><td>...</td><td>0.028</td><td>0.83</td><td>1</td></tr><tr><td>NGVS J12:27:02.60+12:34:47.1</td><td>186.7608440</td><td>12.5797445</td><td>12:27:02.60</td><td>+12:34:47.1</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.030</td><td>0.82</td><td>0</td></tr></tbody></table>
<table><caption>Table 4
(Continued)</caption><thead><tr><th>NGVS ID<br>(1)</th><th>R.A.<br>(deg)<br>(2)</th><th>Decl.<br>(deg)<br>(3)</th><th>R.A.<br>(hms)<br>(4)</th><th>Decl.<br>(dms)<br>(5)</th><th>Class<br>(6)</th><th>VCC ID<br>(7)</th><th>v<br>(km s<sup>-1</sup>)<br>(8)</th><th>δv<br>(km s<sup>-1</sup>)<br>(9)</th><th>Source<br>(10)</th><th>E(B - V)<br>(mag)<br>(11)</th><th>PSF FWHM<br>(arcsec)<br>(12)</th><th>Det. ID<br>(13)</th></tr></thead><tbody><tr><td>NGVS J12:27:03.08+12:33:38.8</td><td>186.7628443</td><td>12.5607787</td><td>12:27:03.08</td><td>+12:33:38.8</td><td>0</td><td>965</td><td>831.0</td><td>7.8</td><td>SDSS</td><td>0.030</td><td>0.82</td><td>3</td></tr><tr><td>NGVS J12:27:03.76+11:31:51.0</td><td>186.7656756</td><td>11.5308283</td><td>12:27:03.76</td><td>+11:31:51.0</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.81</td><td>2</td></tr><tr><td>NGVS J12:27:03.81+12:51:59.2</td><td>186.7658563</td><td>12.8664417</td><td>12:27:03.81</td><td>+12:51:59.2</td><td>0</td><td>967</td><td>1135.8</td><td>30.0</td><td>EVCC</td><td>0.029</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:27:06.07+13:19:25.3</td><td>186.7752955</td><td>13.3236918</td><td>12:27:06.07</td><td>+13:19:25.3</td><td>0</td><td>968</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:27:08.42+13:20:08.7</td><td>186.7850718</td><td>13.3357445</td><td>12:27:08.42</td><td>+13:20:08.7</td><td>0</td><td>972</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:27:10.65+12:46:03.6</td><td>186.7943687</td><td>12.7676781</td><td>12:27:10.65</td><td>+12:46:03.6</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:27:11.20+12:06:52.3</td><td>186.7966853</td><td>12.1145416</td><td>12:27:11.20</td><td>+12:06:52.3</td><td>0</td><td>978</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.79</td><td>0</td></tr><tr><td>NGVS J12:27:11.24+12:02:17.4</td><td>186.7968529</td><td>12.0381804</td><td>12:27:11.24</td><td>+12:02:17.4</td><td>0</td><td>977</td><td>57.3</td><td>17.4</td><td>SDSS</td><td>0.025</td><td>0.79</td><td>0</td></tr><tr><td>NGVS J12:27:12.75+13:13:14.6</td><td>186.8031068</td><td>13.2207154</td><td>12:27:12.75</td><td>+13:13:14.6</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:27:13.34+12:44:05.2</td><td>186.8055801</td><td>12.7347647</td><td>12:27:13.34</td><td>+12:44:05.2</td><td>0</td><td>984</td><td>1893.0</td><td>1.8</td><td>SDSS</td><td>0.029</td><td>0.81</td><td>3</td></tr><tr><td>NGVS J12:27:14.21+12:54:09.6</td><td>186.8092098</td><td>12.9026684</td><td>12:27:14.21</td><td>+12:54:09.6</td><td>0</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.028</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:27:15.01+12:50:55.9</td><td>186.8125281</td><td>12.8488677</td><td>12:27:15.01</td><td>+12:50:55.9</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.79</td><td>2</td></tr><tr><td>NGVS J12:27:15.46+12:39:41.4</td><td>186.8144228</td><td>12.6615036</td><td>12:27:15.46</td><td>+12:39:41.4</td><td>0</td><td>987</td><td>...</td><td>...</td><td>...</td><td>0.030</td><td>0.81</td><td>1</td></tr><tr><td>NGVS J12:27:15.46+13:24:44.8</td><td>186.8144243</td><td>13.4124510</td><td>12:27:15.46</td><td>+13:24:44.8</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.025</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:27:16.78+12:32:07.8</td><td>186.8199207</td><td>12.5355079</td><td>12:27:16.78</td><td>+12:32:07.8</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.028</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:27:19.52+12:13:15.9</td><td>186.8313473</td><td>12.2210825</td><td>12:27:19.52</td><td>+12:13:15.9</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:27:19.62+13:05:13.3</td><td>186.8317334</td><td>13.0870189</td><td>12:27:19.62</td><td>+13:05:13.3</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:27:20.29+11:41:42.8</td><td>186.8345244</td><td>11.6952175</td><td>12:27:20.29</td><td>+11:41:42.8</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.022</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:27:21.11+13:06:40.3</td><td>186.8379500</td><td>13.1111947</td><td>12:27:21.11</td><td>+13:06:40.3</td><td>0</td><td>996</td><td>-27.9</td><td>30.0</td><td>EVCC</td><td>0.029</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:27:22.17+12:04:07.4</td><td>186.8423851</td><td>12.0687121</td><td>12:27:22.17</td><td>+12:04:07.4</td><td>0</td><td>997</td><td>-180.0</td><td>60.0</td><td>EVCC</td><td>0.026</td><td>0.79</td><td>0</td></tr><tr><td>NGVS J12:27:23.46+12:19:54.1</td><td>186.8477404</td><td>12.3317052</td><td>12:27:23.46</td><td>+12:19:54.1</td><td>0</td><td>998</td><td>-120.0</td><td>120.0</td><td>EVCC</td><td>0.028</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:27:25.10+13:24:21.9</td><td>186.8545887</td><td>13.4060779</td><td>12:27:25.10</td><td>+13:24:21.9</td><td>0</td><td>1004</td><td>...</td><td>...</td><td>...</td><td>0.025</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:27:26.91+11:45:11.6</td><td>186.8621220</td><td>11.7532192</td><td>12:27:26.91</td><td>+11:45:11.6</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.024</td><td>0.79</td><td>0</td></tr><tr><td>NGVS J12:27:26.95+11:56:33.4</td><td>186.8623090</td><td>11.9426030</td><td>12:27:26.95</td><td>+11:56:33.4</td><td>1</td><td>1008</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.79</td><td>0</td></tr><tr><td>NGVS J12:27:27.38+12:17:25.0</td><td>186.8640813</td><td>12.2902790</td><td>12:27:27.38</td><td>+12:17:25.0</td><td>0</td><td>1010</td><td>942.6</td><td>1.8</td><td>SDSS</td><td>0.028</td><td>0.81</td><td>3</td></tr><tr><td>NGVS J12:27:29.53+12:16:09.1</td><td>186.8730378</td><td>12.2692073</td><td>12:27:29.53</td><td>+12:16:09.1</td><td>1</td><td>1015</td><td>...</td><td>...</td><td>...</td><td>0.028</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:27:29.55+11:44:04.1</td><td>186.8731248</td><td>11.7344832</td><td>12:27:29.55</td><td>+11:44:04.1</td><td>0</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.022</td><td>0.79</td><td>0</td></tr><tr><td>NGVS J12:27:29.78+12:15:07.2</td><td>186.8740827</td><td>12.2519907</td><td>12:27:29.78</td><td>+12:15:07.2</td><td>0</td><td>1014</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:27:30.38+13:12:55.1</td><td>186.8765759</td><td>13.2153191</td><td>12:27:30.38</td><td>+13:12:55.1</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.031</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:27:32.01+11:36:54.7</td><td>186.8833845</td><td>11.6151815</td><td>12:27:32.01</td><td>+11:36:54.7</td><td>0</td><td>1020</td><td>1380.0</td><td>60.0</td><td>EVCC</td><td>0.025</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:27:33.11+11:31:43.3</td><td>186.8879733</td><td>11.5286815</td><td>12:27:33.11</td><td>+11:31:43.3</td><td>1</td><td>1022</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:27:33.18+11:31:55.7</td><td>186.8882373</td><td>11.5321392</td><td>12:27:33.18</td><td>+11:31:55.7</td><td>1</td><td>1022</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:27:34.39+12:48:12.1</td><td>186.8932954</td><td>12.8033718</td><td>12:27:34.39</td><td>+12:48:12.1</td><td>0</td><td>1023</td><td>...</td><td>...</td><td>...</td><td>0.030</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:27:35.60+12:37:26.3</td><td>186.8983529</td><td>12.6239781</td><td>12:27:35.60</td><td>+12:37:26.3</td><td>0</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:27:37.45+12:22:40.9</td><td>186.9060366</td><td>12.3780296</td><td>12:27:37.45</td><td>+12:22:40.9</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.028</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:27:39.24+12:52:47.6</td><td>186.9134916</td><td>12.8798909</td><td>12:27:39.24</td><td>+12:52:47.6</td><td>0</td><td>1027</td><td>77.1</td><td>30.0</td><td>EVCC</td><td>0.028</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:27:40.49+13:04:44.3</td><td>186.9187168</td><td>13.0789836</td><td>12:27:40.49</td><td>+13:04:44.3</td><td>0</td><td>1030</td><td>806.1</td><td>30.0</td><td>EVCC</td><td>0.029</td><td>0.75</td><td>3</td></tr><tr><td>NGVS J12:27:41.24+12:18:57.2</td><td>186.9218156</td><td>12.3158886</td><td>12:27:41.24</td><td>+12:18:57.2</td><td>0</td><td>1036</td><td>1115.1</td><td>2.7</td><td>SDSS</td><td>0.027</td><td>0.81</td><td>3</td></tr><tr><td>NGVS J12:27:41.67+12:29:16.3</td><td>186.9236052</td><td>12.4878555</td><td>12:27:41.67</td><td>+12:29:16.3</td><td>1</td><td>1037</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:27:42.11+12:05:22.7</td><td>186.9254486</td><td>12.0896455</td><td>12:27:42.11</td><td>+12:05:22.7</td><td>0</td><td>1035</td><td>145.8</td><td>5.1</td><td>SDSS</td><td>0.028</td><td>0.79</td><td>2</td></tr><tr><td>NGVS J12:27:43.43+11:58:04.6</td><td>186.9309633</td><td>11.9679499</td><td>12:27:43.43</td><td>+11:58:04.6</td><td>0</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.025</td><td>0.79</td><td>0</td></tr><tr><td>NGVS J12:27:44.39+12:33:25.9</td><td>186.9349616</td><td>12.5571840</td><td>12:27:44.39</td><td>+12:33:25.9</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:27:44.52+12:59:01.3</td><td>186.9355189</td><td>12.9836833</td><td>12:27:44.52</td><td>+12:59:01.3</td><td>0</td><td>1040</td><td>-143.1</td><td>30.0</td><td>EVCC</td><td>0.028</td><td>0.81</td><td>3</td></tr><tr><td>NGVS J12:27:45.42+12:52:22.5</td><td>186.9392337</td><td>12.8729240</td><td>12:27:45.42</td><td>+12:52:22.5</td><td>0</td><td>1042</td><td>-62.1</td><td>30.0</td><td>EVCC</td><td>0.026</td><td>0.75</td><td>3</td></tr><tr><td>NGVS J12:27:45.65+13:00:31.9</td><td>186.9402024</td><td>13.0088742</td><td>12:27:45.65</td><td>+13:00:31.9</td><td>0</td><td>1043</td><td>-9.5</td><td>30.0</td><td>EVCC</td><td>0.028</td><td>0.81</td><td>3</td></tr><tr><td>NGVS J12:27:46.47+11:44:28.9</td><td>186.9436118</td><td>11.7413747</td><td>12:27:46.47</td><td>+11:44:28.9</td><td>0</td><td>1041</td><td>...</td><td>...</td><td>...</td><td>0.024</td><td>0.79</td><td>0</td></tr></tbody></table>
<table><caption>Table 4
(Continued)</caption><thead><tr><th>NGVS ID<br>(1)</th><th>R.A.<br>(deg)<br>(2)</th><th>Decl.<br>(deg)<br>(3)</th><th>R.A.<br>(hms)<br>(4)</th><th>Decl.<br>(dms)<br>(5)</th><th>Class<br>(6)</th><th>VCC ID<br>(7)</th><th>v<br>(km s<sup>-1</sup>)<br>(8)</th><th>δv<br>(km s<sup>-1</sup>)<br>(9)</th><th>Source<br>(10)</th><th>E(B - V)<br>(mag)<br>(11)</th><th>PSF FWHM<br>(arcsec)<br>(12)</th><th>Det. ID<br>(13)</th></tr></thead><tbody><tr><td>NGVS J12:27:49.49+12:29:58.7</td><td>186.9561903</td><td>12.4996399</td><td>12:27:49.49</td><td>+12:29:58.7</td><td>0</td><td>1046</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:27:53.17+12:22:58.8</td><td>186.9715492</td><td>12.3829911</td><td>12:27:53.17</td><td>+12:22:58.8</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:27:53.42+12:58:22.9</td><td>186.9725795</td><td>12.9730224</td><td>12:27:53.42</td><td>+12:58:22.9</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:27:53.57+12:17:35.8</td><td>186.9732042</td><td>12.2932664</td><td>12:27:53.57</td><td>+12:17:35.8</td><td>0</td><td>1047</td><td>724.5</td><td>30.0</td><td>EVCC</td><td>0.027</td><td>0.72</td><td>3</td></tr><tr><td>NGVS J12:27:54.56+12:36:16.2</td><td>186.9773157</td><td>12.6045047</td><td>12:27:54.56</td><td>+12:36:16.2</td><td>1</td><td>1051</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:27:55.22+12:22:09.5</td><td>186.9800778</td><td>12.3692963</td><td>12:27:55.22</td><td>+12:22:09.5</td><td>0</td><td>1052</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.81</td><td>1</td></tr><tr><td>NGVS J12:28:00.33+11:30:34.7</td><td>187.0013675</td><td>11.5096373</td><td>12:28:00.33</td><td>+11:30:34.7</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:00.44+11:56:59.6</td><td>187.0018514</td><td>11.9498934</td><td>12:28:00.44</td><td>+11:56:59.6</td><td>0</td><td>1059</td><td>2250.0</td><td>420.0</td><td>EVCC</td><td>0.026</td><td>0.79</td><td>0</td></tr><tr><td>NGVS J12:28:03.74+12:46:41.2</td><td>187.0155701</td><td>12.7781194</td><td>12:28:03.74</td><td>+12:46:41.2</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.025</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:04.79+11:36:16.5</td><td>187.0199746</td><td>11.6045821</td><td>12:28:04.79</td><td>+11:36:16.5</td><td>1</td><td>1063</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:28:05.92+12:50:15.5</td><td>187.0246748</td><td>12.8376481</td><td>12:28:05.92</td><td>+12:50:15.5</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.024</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:06.53+12:53:53.3</td><td>187.0272120</td><td>12.8981447</td><td>12:28:06.53</td><td>+12:53:53.3</td><td>0</td><td>1069</td><td>2327.4</td><td>20.4</td><td>SDSS</td><td>0.025</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:06.77+12:58:43.2</td><td>187.0282104</td><td>12.9786644</td><td>12:28:06.77</td><td>+12:58:43.2</td><td>0</td><td>1070</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:07.90+12:24:07.9</td><td>187.0329343</td><td>12.4021844</td><td>12:28:07.90</td><td>+12:24:07.9</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.028</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:08.61+12:05:35.8</td><td>187.0358723</td><td>12.0932857</td><td>12:28:08.61</td><td>+12:05:35.8</td><td>0</td><td>1073</td><td>1923.3</td><td>3.9</td><td>SDSS</td><td>0.028</td><td>0.79</td><td>3</td></tr><tr><td>NGVS J12:28:10.07+12:43:29.4</td><td>187.0419691</td><td>12.7248463</td><td>12:28:10.07</td><td>+12:43:29.4</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.024</td><td>0.80</td><td>2</td></tr><tr><td>NGVS J12:28:10.28+12:48:32.2</td><td>187.0428223</td><td>12.8089317</td><td>12:28:10.28</td><td>+12:48:32.2</td><td>1</td><td>1077</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:12.24+11:58:13.3</td><td>187.0510001</td><td>11.9703637</td><td>12:28:12.24</td><td>+11:58:13.3</td><td>1</td><td>1083</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.79</td><td>0</td></tr><tr><td>NGVS J12:28:12.60+12:45:33.9</td><td>187.0524909</td><td>12.7594205</td><td>12:28:12.60</td><td>+12:45:33.9</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:12.81+13:00:54.0</td><td>187.0533877</td><td>13.0150039</td><td>12:28:12.81</td><td>+13:00:54.0</td><td>0</td><td>1081</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:12.86+12:54:56.5</td><td>187.0535830</td><td>12.9157083</td><td>12:28:12.86</td><td>+12:54:56.5</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.024</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:14.87+11:47:23.6</td><td>187.0619636</td><td>11.7898823</td><td>12:28:14.87</td><td>+11:47:23.6</td><td>0</td><td>1087</td><td>662.7</td><td>4.8</td><td>SDSS</td><td>0.027</td><td>0.79</td><td>3</td></tr><tr><td>NGVS J12:28:15.41+12:33:37.2</td><td>187.0641948</td><td>12.5603200</td><td>12:28:15.41</td><td>+12:33:37.2</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.024</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:15.85+12:52:12.0</td><td>187.0660464</td><td>12.8700124</td><td>12:28:15.85</td><td>+12:52:12.0</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.022</td><td>0.80</td><td>2</td></tr><tr><td>NGVS J12:28:18.74+11:42:00.9</td><td>187.0780927</td><td>11.7002572</td><td>12:28:18.74</td><td>+11:42:00.9</td><td>0</td><td>1093</td><td>1477.5</td><td>22.5</td><td>SDSS</td><td>0.027</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:28:20.08+13:18:37.2</td><td>187.0836649</td><td>13.3103346</td><td>12:28:20.08</td><td>+13:18:37.2</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:20.18+13:21:35.5</td><td>187.0840982</td><td>13.3598640</td><td>12:28:20.18</td><td>+13:21:35.5</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:21.59+12:38:45.4</td><td>187.0899604</td><td>12.6459429</td><td>12:28:21.59</td><td>+12:38:45.4</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:21.66+12:08:04.0</td><td>187.0902655</td><td>12.1344556</td><td>12:28:21.66</td><td>+12:08:04.0</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.028</td><td>0.79</td><td>2</td></tr><tr><td>NGVS J12:28:23.37+11:34:46.9</td><td>187.0973594</td><td>11.5796867</td><td>12:28:23.37</td><td>+11:34:46.9</td><td>0</td><td>1100</td><td>...</td><td>...</td><td>...</td><td>0.028</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:23.64+13:11:44.7</td><td>187.0985017</td><td>13.1957565</td><td>12:28:23.64</td><td>+13:11:44.7</td><td>0</td><td>1101</td><td>1740.0</td><td>60.0</td><td>EVCC</td><td>0.023</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:26.26+12:20:45.2</td><td>187.1094119</td><td>12.3458876</td><td>12:28:26.26</td><td>+12:20:45.2</td><td>0</td><td>1103</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.81</td><td>2</td></tr><tr><td>NGVS J12:28:27.72+12:33:29.9</td><td>187.1154978</td><td>12.5582965</td><td>12:28:27.72</td><td>+12:33:29.9</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:28.06+12:49:25.3</td><td>187.1169051</td><td>12.8236946</td><td>12:28:28.06</td><td>+12:49:25.3</td><td>0</td><td>1104</td><td>1708.2</td><td>12.3</td><td>SDSS</td><td>0.021</td><td>0.81</td><td>3</td></tr><tr><td>NGVS J12:28:29.72+11:58:19.6</td><td>187.1238527</td><td>11.9721197</td><td>12:28:29.72</td><td>+11:58:19.6</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.79</td><td>0</td></tr><tr><td>NGVS J12:28:31.15+11:31:59.9</td><td>187.1298077</td><td>11.5333177</td><td>12:28:31.15</td><td>+11:31:59.9</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.030</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:31.99+12:59:16.6</td><td>187.1332896</td><td>12.9879573</td><td>12:28:31.99</td><td>+12:59:16.6</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.022</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:32.13+12:32:09.7</td><td>187.1338572</td><td>12.5360140</td><td>12:28:32.13</td><td>+12:32:09.7</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:32.40+11:44:40.7</td><td>187.1350073</td><td>11.7446286</td><td>12:28:32.40</td><td>+11:44:40.7</td><td>0</td><td>1115</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.80</td><td>2</td></tr><tr><td>NGVS J12:28:35.75+12:10:57.2</td><td>187.1489377</td><td>12.1825527</td><td>12:28:35.75</td><td>+12:10:57.2</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:28:36.07+11:40:16.5</td><td>187.1502844</td><td>11.6712580</td><td>12:28:36.07</td><td>+11:40:16.5</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.029</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:28:37.88+12:51:42.0</td><td>187.1578363</td><td>12.8616713</td><td>12:28:37.88</td><td>+12:51:42.0</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.020</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:39.87+12:58:40.5</td><td>187.1661420</td><td>12.9779291</td><td>12:28:39.87</td><td>+12:58:40.5</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.022</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:41.71+12:54:57.2</td><td>187.1737961</td><td>12.9158877</td><td>12:28:41.71</td><td>+12:54:57.2</td><td>0</td><td>1122</td><td>458.4</td><td>3.3</td><td>SDSS</td><td>0.020</td><td>0.80</td><td>3</td></tr><tr><td>NGVS J12:28:42.66+12:32:59.4</td><td>187.1777602</td><td>12.5498411</td><td>12:28:42.66</td><td>+12:32:59.4</td><td>0</td><td>1123</td><td>1593.9</td><td>27.9</td><td>MMT</td><td>0.022</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:43.31+11:45:18.1</td><td>187.1804470</td><td>11.7550324</td><td>12:28:43.31</td><td>+11:45:18.1</td><td>0</td><td>1125</td><td>162.0</td><td>2.4</td><td>SDSS</td><td>0.030</td><td>0.80</td><td>3</td></tr></tbody></table>
<table><caption>Table 4
(Continued)</caption><thead><tr><th>NGVS ID<br>(1)</th><th>R.A.<br>(deg)<br>(2)</th><th>Decl.<br>(deg)<br>(3)</th><th>R.A.<br>(hms)<br>(4)</th><th>Decl.<br>(dms)<br>(5)</th><th>Class<br>(6)</th><th>VCC ID<br>(7)</th><th>v<br>(km s<sup>-1</sup>)<br>(8)</th><th>δ v<br>(km s<sup>-1</sup>)<br>(9)</th><th>Source<br>(10)</th><th>E(B - V)<br>(mag)<br>(11)</th><th>PSF FWHM<br>(arcsec)<br>(12)</th><th>Det. ID<br>(13)</th></tr></thead><tbody><tr><td>NGVS J12:28:44.65+11:59:37.2</td><td>187.1860303</td><td>11.9936531</td><td>12:28:44.65</td><td>+11:59:37.2</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.79</td><td>0</td></tr><tr><td>NGVS J12:28:44.91+12:48:34.3</td><td>187.1871314</td><td>12.8095314</td><td>12:28:44.91</td><td>+12:48:34.3</td><td>0</td><td>1129</td><td>12.0</td><td>90.0</td><td>EVCC</td><td>0.020</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:45.79+12:01:18.6</td><td>187.1907795</td><td>12.0218433</td><td>12:28:45.79</td><td>+12:01:18.6</td><td>0</td><td>1131</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.79</td><td>0</td></tr><tr><td>NGVS J12:28:46.92+12:38:31.5</td><td>187.1954927</td><td>12.6420948</td><td>12:28:46.92</td><td>+12:38:31.5</td><td>0</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.021</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:47.37+12:49:48.5</td><td>187.1973668</td><td>12.8301515</td><td>12:28:47.37</td><td>+12:49:48.5</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.020</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:48.93+11:53:10.4</td><td>187.2038858</td><td>11.8862171</td><td>12:28:48.93</td><td>+11:53:10.4</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.79</td><td>0</td></tr><tr><td>NGVS J12:28:49.11+12:07:54.5</td><td>187.2046093</td><td>12.1318006</td><td>12:28:49.11</td><td>+12:07:54.5</td><td>0</td><td>1136</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:28:49.98+12:47:46.7</td><td>187.2082412</td><td>12.7963051</td><td>12:28:49.98</td><td>+12:47:46.7</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.020</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:51.02+12:07:09.0</td><td>187.2125677</td><td>12.1191772</td><td>12:28:51.02</td><td>+12:07:09.0</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:28:51.07+11:34:24.8</td><td>187.2128117</td><td>11.5735634</td><td>12:28:51.07</td><td>+11:34:24.8</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.030</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:51.30+11:57:26.9</td><td>187.2137575</td><td>11.9574803</td><td>12:28:51.30</td><td>+11:57:26.9</td><td>1</td><td>1139</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.79</td><td>0</td></tr><tr><td>NGVS J12:28:52.76+12:44:12.3</td><td>187.2198533</td><td>12.7367595</td><td>12:28:52.76</td><td>+12:44:12.3</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.021</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:53.71+13:11:51.2</td><td>187.2237804</td><td>13.1975448</td><td>12:28:53.71</td><td>+13:11:51.2</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:53.73+12:58:53.7</td><td>187.2238681</td><td>12.9815923</td><td>12:28:53.73</td><td>+12:58:53.7</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.020</td><td>0.81</td><td>0</td></tr><tr><td>NGVS J12:28:55.57+12:42:24.6</td><td>187.2315384</td><td>12.7068409</td><td>12:28:55.57</td><td>+12:42:24.6</td><td>0</td><td>1143</td><td>...</td><td>...</td><td>...</td><td>0.021</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:55.65+12:25:42.3</td><td>187.2318611</td><td>12.4284270</td><td>12:28:55.65</td><td>+12:25:42.3</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.82</td><td>1</td></tr><tr><td>NGVS J12:28:56.04+12:42:54.8</td><td>187.2335005</td><td>12.7152281</td><td>12:28:56.04</td><td>+12:42:54.8</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.021</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:56.13+13:26:42.2</td><td>187.2338786</td><td>13.4450518</td><td>12:28:56.13</td><td>+13:26:42.2</td><td>0</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.84</td><td>0</td></tr><tr><td>NGVS J12:28:57.56+13:14:31.0</td><td>187.2398351</td><td>13.2419339</td><td>12:28:57.56</td><td>+13:14:31.0</td><td>0</td><td>1146</td><td>635.4</td><td>30.0</td><td>EVCC</td><td>0.023</td><td>0.80</td><td>3</td></tr><tr><td>NGVS J12:28:57.68+11:57:20.2</td><td>187.2403374</td><td>11.9556017</td><td>12:28:57.68</td><td>+11:57:20.2</td><td>1</td><td>1147</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:28:58.14+12:39:42.2</td><td>187.2422494</td><td>12.6617298</td><td>12:28:58.14</td><td>+12:39:42.2</td><td>0</td><td>1148</td><td>1416.3</td><td>3.3</td><td>SDSS</td><td>0.021</td><td>0.82</td><td>3</td></tr><tr><td>NGVS J12:28:58.84+12:54:28.8</td><td>187.2451828</td><td>12.9079984</td><td>12:28:58.84</td><td>+12:54:28.8</td><td>0</td><td>1149</td><td>...</td><td>...</td><td>...</td><td>0.020</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:28:59.15+12:02:30.4</td><td>187.2464597</td><td>12.0417734</td><td>12:28:59.15</td><td>+12:02:30.4</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:28:59.50+11:55:23.4</td><td>187.2479078</td><td>11.9231733</td><td>12:28:59.50</td><td>+11:55:23.4</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:28:59.82+12:38:54.2</td><td>187.2492426</td><td>12.6483894</td><td>12:28:59.82</td><td>+12:38:54.2</td><td>0</td><td>1153</td><td>990.0</td><td>60.0</td><td>EVCC</td><td>0.021</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:29:01.16+12:33:30.8</td><td>187.2548145</td><td>12.5585684</td><td>12:29:01.16</td><td>+12:33:30.8</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.022</td><td>0.83</td><td>0</td></tr><tr><td>NGVS J12:29:01.17+12:25:50.2</td><td>187.2548802</td><td>12.4305987</td><td>12:29:01.17</td><td>+12:25:50.2</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.82</td><td>2</td></tr><tr><td>NGVS J12:29:02.02+12:26:05.5</td><td>187.2584302</td><td>12.4348537</td><td>12:29:02.02</td><td>+12:26:05.5</td><td>0</td><td>1157</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:29:03.01+13:11:01.7</td><td>187.2625503</td><td>13.1838010</td><td>12:29:03.01</td><td>+13:11:01.7</td><td>0</td><td>1158</td><td>1932.3</td><td>30.0</td><td>EVCC</td><td>0.023</td><td>0.77</td><td>3</td></tr><tr><td>NGVS J12:29:03.26+12:05:58.9</td><td>187.2635749</td><td>12.0997045</td><td>12:29:03.26</td><td>+12:05:58.9</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:29:05.13+12:09:13.6</td><td>187.2713899</td><td>12.1537795</td><td>12:29:05.13</td><td>+12:09:13.6</td><td>0</td><td>1162</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:29:05.42+12:01:52.5</td><td>187.2725840</td><td>12.0312573</td><td>12:29:05.42</td><td>+12:01:52.5</td><td>0</td><td>1161</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:29:09.24+12:29:45.6</td><td>187.2884942</td><td>12.4960042</td><td>12:29:09.24</td><td>+12:29:45.6</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.022</td><td>0.83</td><td>0</td></tr><tr><td>NGVS J12:29:09.56+12:33:29.3</td><td>187.2898510</td><td>12.5581312</td><td>12:29:09.56</td><td>+12:33:29.3</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.022</td><td>0.83</td><td>0</td></tr><tr><td>NGVS J12:29:11.82+13:09:48.7</td><td>187.2992339</td><td>13.1635324</td><td>12:29:11.82</td><td>+13:09:48.7</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:29:12.31+11:31:11.9</td><td>187.3013108</td><td>11.5199692</td><td>12:29:12.31</td><td>+11:31:11.9</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.030</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:29:14.85+12:58:41.7</td><td>187.3118929</td><td>12.9782469</td><td>12:29:14.85</td><td>+12:58:41.7</td><td>0</td><td>1173</td><td>2413.8</td><td>13.5</td><td>SDSS</td><td>0.020</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:29:17.55+13:04:42.6</td><td>187.3231217</td><td>13.0785018</td><td>12:29:17.55</td><td>+13:04:42.6</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.80</td><td>2</td></tr><tr><td>NGVS J12:29:19.28+12:22:37.2</td><td>187.3303288</td><td>12.3770123</td><td>12:29:19.28</td><td>+12:22:37.2</td><td>0</td><td>1177</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.82</td><td>0</td></tr><tr><td>NGVS J12:29:20.27+12:01:16.4</td><td>187.3344524</td><td>12.0212176</td><td>12:29:20.27</td><td>+12:01:16.4</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.026</td><td>0.80</td><td>2</td></tr><tr><td>NGVS J12:29:20.73+13:22:12.0</td><td>187.3363629</td><td>13.3700055</td><td>12:29:20.73</td><td>+13:22:12.0</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.027</td><td>0.84</td><td>0</td></tr><tr><td>NGVS J12:29:21.55+12:28:03.4</td><td>187.3397966</td><td>12.4676135</td><td>12:29:21.55</td><td>+12:28:03.4</td><td>1</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.84</td><td>0</td></tr><tr><td>NGVS J12:29:22.40+11:49:17.7</td><td>187.3433310</td><td>11.8215864</td><td>12:29:22.40</td><td>+11:49:17.7</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.028</td><td>0.80</td><td>0</td></tr><tr><td>NGVS J12:29:23.52+12:27:02.9</td><td>187.3479850</td><td>12.4508043</td><td>12:29:23.52</td><td>+12:27:02.9</td><td>0</td><td>1185</td><td>448.2</td><td>8.1</td><td>SDSS</td><td>0.023</td><td>0.84</td><td>3</td></tr><tr><td>NGVS J12:29:26.27+13:06:50.3</td><td>187.3594508</td><td>13.1139690</td><td>12:29:26.27</td><td>+13:06:50.3</td><td>2</td><td>...</td><td>...</td><td>...</td><td>...</td><td>0.023</td><td>0.81</td><td>2</td></tr><tr><td>NGVS J12:29:28.67+12:29:46.3</td><td>187.3694547</td><td>12.4962070</td><td>12:29:28.67</td><td>+12:29:46.3</td><td>0</td><td>1191</td><td>7.4</td><td>60.0</td><td>EVCC</td><td>0.022</td><td>0.84</td><td>0</td></tr></tbody></table>