# A Census of Compact Elliptical Galaxies in the Coma Cluster

Aleksandra V Sharonova, Kirill A Grishin, Igor V Chilingarian, Gary A Mamon, Nelson Caldwell, Daniel Fabricant

► To cite this version:

Aleksandra V Sharonova, Kirill A Grishin, Igor V Chilingarian, Gary A Mamon, Nelson Caldwell, et al. A Census of Compact Elliptical Galaxies in the Coma Cluster. The Astrophysical Journal, 2025, 993 (2), pp.229. 10.3847/1538-4357/ae070d hal-05370357

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# A Census of Compact Elliptical Galaxies in the Coma Cluster

Aleksandra V. Sharonova<fnref n="1" />,<fnref n="2" /> ID, Kirill A. Grishin<fnref n="2" />,<fnref n="3" /> ID, Igor V. Chilingarian<fnref n="2" />,<fnref n="4" /> ID, Gary A. Mamon<fnref n="5" /> ID, Nelson Caldwell<fnref n="4" /> ID, and Daniel Fabricant<fnref n="4" /> ID

## Abstract

Compact elliptical (cE) galaxies are compact stellar systems with stellar masses of $10^8 \le M_*/M_{\odot} \le 10^{10}$ and radii typically <0.6 kpc. Here we investigate the properties of 13 cE galaxies in the Coma cluster, 6 of which are newly identified. Our goal in this paper is to explore whether these cEs form directly in the cluster environment or are preprocessed in small groups before infalling. We find that preprocessing in groups significantly contributes to the cE population in the Coma cluster. We analyze Hyper Suprime-Cam g-band Coma images and validate our photometric measurements through comparison with Hubble Space Telescope data. We also analyze spectroscopic data from the Dark Energy Spectroscopic Instrument. We significantly expand the known cE population in the Coma cluster through joint photometric and spectroscopic selection. We identify a subpopulation of cEs that likely formed in infalling groups, through their association with host galaxies, their positions on the caustic diagram, and their projected phase-space trajectories. We estimate that the central cE population will increase by up to 30% within the next 0.4 Gyr, highlighting the important role of preprocessing in cE evolution.

*Unified Astronomy Thesaurus concepts: Compact galaxies (285); Coma Cluster (270); Galaxy evolution (594); Galaxy groups (597)*

## 1. Introduction

Compact elliptical (cE) galaxies represent a relatively rare class of compact stellar systems (CSSs) in the local Universe. They have stellar masses of $10^8 \le M_*/M_{\odot} \le 10^{10}$ and radii typically <0.6 kpc, indicating high stellar densities. Studies of Messier 32 (W. Baade 1944; S. M. Faber 1973) led B. Binggeli et al. (1984) to identify cE galaxies as a distinct class. We adopt this original definition of cEs and distinguish them from massive compact galaxies—known as red nuggets, identified by P. G. van Dokkum et al. (2008), which typically have higher stellar masses exceeding $10^{11} M_{\odot}$ (I. Damjanov et al. 2009, 2014; A. Ferré-Mateu et al. 2017). M. J. Drinkwater et al. (2000) found even smaller unresolved ultracompact dwarf (UCD) galaxies with old stellar populations in the Fornax cluster. Later, cEs were discovered in the A1689 (S. Mieske et al. 2005) and A496 (I. Chilingarian et al. 2007a) clusters. J. Price et al. (2009) discovered and analyzed a sample of 7 cEs in the Coma cluster using photometric observations from the Hubble Space Telescope (HST) Treasury Survey and spectral data from MMT/Hectospec. I. Chilingarian et al. (2009) identified 21 cEs in clusters using HST-WFPC2 photometry and SCORPIO 6-m BTA spectroscopy. I. Chilingarian & I. Zolotukhin (2015) identified a sample of 195 cEs combining Sloan Digital Sky Survey (SDSS) photometric and spectroscopic data with GALaxy Evolution eXplorer UV data.

Although wide-field ground-based observations have identified a significant number of cE candidates, with typical 1" seeing corresponding to ~0.5 kpc at 100 Mpc, space observatories are required for cE structure characterization. Spectroscopic redshifts are necessary to precisely associate cEs with host groups or clusters.

A combination of photometric and spectroscopic surveys has allowed us to place cEs in the context of CSSs, a category that also includes UCDs and globular clusters. Most cEs are intermediate in the scaling relations (size–luminosity ($R_c$–L), velocity dispersion–luminosity ($\sigma_*$–L), and metallicity–luminosity ([Fe/H]–L) between UCDs and more massive early-type galaxies (ETGs; I. V. Chilingarian & G. A. Mamon 2008; D. A. Forbes et al. 2014; M. A. Norris et al. 2014; J. Janz et al. 2016). cEs and UCDs may form similarly through tidal stripping. UCDs are tidally stripped dwarf or intermediate-mass nucleated galaxies and contain nuclear star clusters surrounded by small stellar envelopes that survived stripping. Tidally stripped dwarf galaxies lack sufficient central stellar density to become cEs. Rather, cEs are the stripped cores of elliptical (S. M. Faber 1973) or compact disk galaxy bulges (K. Bekki et al. 2001; A. W. Graham 2002; M. J. Drinkwater et al. 2003). Some recently formed cEs show tidal tails, clear signatures of their host galaxy interactions (A. P. Huxor et al. 2011; S. Paudel & C. H. Ree 2014; I. Chilingarian & I. Zolotukhin 2015). A CSS inherits some properties of its tidally stripped progenitor (a larger and more massive galaxy) including central black holes more massive than expected for their stellar mass (for UCDs: A. C. Seth et al. 2014; C. P. Ahn et al. 2017; A. V. Afanasiev et al. 2018; R. Pechetti et al. 2022; for cEs: C. Barber et al. 2016; S. Paudel et al. 2016; R. Pechetti et al. 2017). An alternate, intrinsic formation scenario

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<footnote n="1">¹ Faculty of Space Research, M.V. Lomonosov Moscow State University, 1 Leninskiye Gory, 119991 Moscow, Russia; asharonova@voxastro.org</footnote>

<footnote n="2">² Sternberg Astronomical Institute, M.V. Lomonosov Moscow State University, 13 Universitetsky prospect, 119992 Moscow, Russia; grishin@voxastro.org</footnote>

<footnote n="3">³ Universite Paris Cite, CNRS, Astroparticule et Cosmologie, F-75013 Paris, France</footnote>

<footnote n="4">⁴ Center for Astrophysics—Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA</footnote>

<footnote n="5">⁵ Institut d'Astrophysique de Paris (UMR7095: CNRS & Sorbonne Université), 98 bis Bd Arago, 75014, Paris, France</footnote>

<footnote>Received 2025 May 16; revised 2025 September 10; accepted 2025 September 11; published 2025 November 6</footnote>
postulates that some UCDs represent the high-mass end of the globular cluster luminosity function (N. Murray 2009; R. C. Brüns et al. 2011; S. Mieske et al. 2012) and that cEs are the lowest-mass ETGs (A. Wirth & J. S. Gallagher 1984; J. L. Nieto & P. Prugniel 1987; J. Kormendy et al. 2009; J. Kormendy & R. Bender 2012) formed via gradual buildup of stellar mass (N. Martinović & M. Micic 2017; S. Deeley et al. 2023) and mergers of nuclear star clusters (F. Urrutia Zapata et al. 2019).

UCD and cE stellar populations provide additional clues about their evolutionary pathways. UCDs with higher metallicities likely formed through tidal stripping of intermediate-mass galaxies, whereas UCDs with lower metallicity (consistent with those observed in globular clusters) have intrinsic origins (I. V. Chilingarian et al. 2008a, 2011; K. J. Francis et al. 2012). cEs forming by tidal stripping exhibit high metallicities for their mass, old stellar ages, and are often outliers in the [Fe/H]–L relation (I. V. Chilingarian & G. Bergond 2010; J. Janz et al. 2016; A. Ferré-Mateu et al. 2021). Intrinsically formed cEs, on the other hand, fall on the [Fe/H]–L relation for ETGs (S. Deeley et al. 2023).

A substantial fraction of the observed cEs are found in clusters (I. Chilingarian & I. Zolotukhin 2015), but probably not all cluster cEs formed by tidal stripping in the cluster/cD potential; some galaxies could be processed before infall (Y. Fujita 2004). Some studies (S. L. McGee et al. 2009; A. Dressler et al. 2013; S. Han et al. 2018) suggest that close to half the cluster members were accreted as members of galaxy groups.

In this work, we study the origin of the cE population in the Coma cluster with combined photometric and spectroscopic data sets. The photometric data sets consist of deep archival g-band Hyper Suprime-Cam (HSC; S. Miyazaki et al. 2018) images obtained in subarcsec seeing. Deep F475W and F814W HST Advanced Camera for Surveys Coma treasury survey images (C. Hoyos et al. 2011) partially overlap the HSC fields. The spectroscopic data sets include Dark Energy Spectroscopic Instrument (DESI) Early Data Release (EDR; DESI Collaboration et al. 2022) and MMT/Binospec spectra. We identify a cE subpopulation that may have been preprocessed in groups before entering the cluster environment, now contributing to the cE population in the cluster center.

Throughout, we assume that the distance to the Coma cluster is 101 Mpc (E. L. Łokas & G. A. Mamon 2003), the angular scale—0.49 kpc arcsec⁻¹, $H_0$ = 70 km s⁻¹ Mpc⁻¹, over density relative to critical, $\Delta_c$ = 102, and the Coma cluster center is coincident with NGC 4874 on the plane of the sky, with a velocity of 7000 km s⁻¹ (E. L. Łokas & G. A. Mamon 2003). All magnitudes are in the AB system (J. B. Oke & J. E. Gunn 1983), and all uncertainties are quoted at the 1σ level unless stated otherwise.

# 2. Observational Data

## 2.1. HSC Data Set

Our cE selection is based on photometry from an archival HSC g-band Coma cluster data set. The data set contains 175 frames with 240 s exposures and 198 frames with 60 s exposures mostly obtained in 2016 and 2017. The images extend to radius 1.7 deg (2.96 Mpc), or $1.23R_{vir}$ (M. Ho et al. 2022), and cover 13.4 deg² with a 3σ magnitude limit of 25.6.

The point-spread function (PSF) ranges from 0.59 to 1.27 FWHM, with a mean of 0.80.

The archival HSC frames were reduced with the hscPipe pipeline.<fnref n="6" /> (J. Bosch et al. 2018) This pipeline returns a fully calibrated data set with an astrometric solution and a sky background map. However, the pipeline sky background subtraction leads to dark artifacts around large galaxies, close groups and interacting intermediate-size galaxies, and over-subtracts intracluster light. These artifacts bias the measured structural properties of the cluster members. We built a better model of the sky background using observations of fields free of bright stars or very extended galaxies collected during the same observing runs (I. Chilingarian et al. 2023). We will provide details of our data reduction techniques in a dedicated publication. Figure 1 shows the HSC g-band mosaic, illustrating the spatial coverage and location of the selected targets.

## 2.2. DESI EDR Spectra for Coma Cluster

The DESI survey observed the Coma cluster with its multiobject spectrograph (DESI Collaboration et al. 2022) during the Survey Validation Program 3 (SV3). These data were published in the EDR (DESI Collaboration et al. 2024a). The mean fiber allocation fraction was 99% for the Bright Galaxy Survey (BGS; C. Hahn et al. 2023) during SV3 (A. D. Myers et al. 2023). This survey includes three Coma cluster components: (i) a complete magnitude-limited sample of galaxies (BGS Bright) with $r < 19.5$; (ii) a sample (BGS Faint) of galaxies with $19.5 < r < 20.175$ mag; and (iii) a low-z AGN sample (a small contributor to the Coma galaxy sample). The BGS Bright sample probes the high-luminosity end of the cE population because it is complete to $M_r < -15.5$ mag. The BGS Faint sample reaches 75%-85% completeness for $-15.5 < M_r < -14.8$ mag (C. Hahn et al. 2023) at the Coma cluster redshift.

Within the redshift range of $0.01 < z < 0.037$, extending to $\gtrsim 4\sigma$ of the Coma cluster's velocity dispersion ($\sigma \sim 1000$ km s⁻¹; J. Sohn et al. 2017), the DESI EDR contains 3292 spectra.

## 2.3. MMT Binospec Spectra

Several Coma cluster fields were observed using the Binospec spectrograph at the 6.5 m MMT in multiobject slitmask mode (mask IDs: Coma1, Coma3, ComaA, ComaB, Coma_dE2a, Coma_dE2b, Coma_dE3a, Coma_dE3b) in 2017–2022. These data sets were obtained as part of the observing programs SAO-6, SAO-9-20a, SAO-7-21b, SAO-9-22A. These observations were reduced with the Binospec pipeline (I. Chilingarian et al. 2019; J. Kansky et al. 2019) in a special mode that masks extended galaxies that would contaminate the night sky model. The pipeline produces sky-subtracted, rectified, and wavelength-resampled 2D long-slit spectra calibrated in absolute fluxes, plus the corresponding flux uncertainties. We use the Binospec spectra to validate the DESI EDR velocity dispersions and stellar population estimates and for observations of two sample galaxies obtained with masks ComaA<fnref n="7" /> and Coma_dE2a. Coma_dE2a was observed on 2019 May 26 and 28 and 2020 May 20. We used the 1000 g mm⁻¹ grating, with spectral range

<footnote n="6">⁶ https://hsc.mtk.nao.ac.jp/pipedoc/pipedoc_8_e/index.html</footnote>

<footnote n="7">⁷ Described in K. A. Grishin et al. (2021).</footnote>
<figure><img src="image_3.png" /><figcaption>**Figure 1.** The position of cE galaxies from our sample in the Coma cluster. Galaxies from J. Price et al. (2009) are marked as pink squares, and one galaxy from I. Chilingarian et al. (2009) and A. M. Cody et al. (2009) is marked as a red square.</figcaption></figure>

3805–5310 Å and a mean spectral resolving power of R = 5000. The 2019 and 2020 exposure times were 2 hr per mask, with exposure times of 4 hr for coadded frames.

## 3. Data Analysis

### 3.1. Automated Surface Photometry with SourceXtractor++

We used the SOURCEXTRACTOR++ package (E. Bertin et al. 2020; M. Kümmel et al. 2022) to obtain the photometric properties of the galaxies in the reduced HSC images. The code detects objects in the image and calculates initial parameters guesses and then fits a predefined combination of

light profile components for all detected objects. We specify parameters for object extraction in the object detection configuration file. Object extraction including background subtraction, filtering, segmentation, and object detection proceeds as in the earlier the SOURCEXTRACTOR package (E. Bertin & S. Arnouts 1996). We set the detection threshold to 1.5 standard deviations above the background and the minimum detection area to 5 pixels.

The photometric modeling configuration file is written in PYTHON. It includes a set of photometric components, free ranges of their parameters, limits on the light fraction between the different components, a list of fixed parameters, and a list
of parameters to be included to the output catalog. The parameter ranges also depend on initial guess values from the object extraction.

We use a combination of single Sérsic and PSF models motivated by previous studies of Coma cluster dwarf galaxies showing that the galaxy shapes cannot fit with a single Sérsic component (J. T. C. G. Head et al. 2015). For the Sérsic profile we used the following parameters ranges: effective radius from 0.4 to 10 v (where v is the initial guess) with a geometric grid, a Sérsic index from 0.5 to 5 (linear steps), and an axis ratio from 0.1 to 1 (geometric steps). We created the PSF frame using the PSFEX package (E. Bertin 2011), and the data reduction pipeline provided an error frame for the weight image.

## 3.2. Analysis of DESI and Binospec Spectra

We used the NBURSTS (I. Chilingarian et al. 2007b) package to perform full spectral fitting in pixel space for a sample of DESI EDR spectra. Each spectrum was modeled in the wavelength range of 3796–9800 Å using X-Shooter simple stellar population (SSP) templates (K. Verro et al. 2022).

The stellar population models include a multiplicative fifth-order Legendre polynomial term to fit the continuum. We account for potential emission lines by including lines with the line-of-sight (LOS) velocity distribution in addition to the stellar population models. In NBURSTS the models are convolved with the line-spread function (LSF) profile. We took the LSF profiles from the *B_RESOLUTION*, *R_RESOLUTION*, and *Z_RESOLUTION* header/data units (HDUs from the COADD-*[^8]*FITS files provided by the DESI survey approximated by Gauss-Hermite polynomials. The DESI spectral resolution is nearly constant with $\sigma \approx 0.4$ Å, corresponding to 70 km s⁻¹ at 4000 Å and 30 km s⁻¹ at 9500 Å.

We also model Binospec 2D slit spectra with the NBURSTS package. We applied adaptive binning along the slit to achieve a minimum signal-to-noise ratio in the inner and outer parts of each galaxy (see the complete description of the Binospec analysis in K. A. Grishin et al. 2021). We use the PEGASE-HR (D. Le Borgne et al. 2004) set of SSP templates, a 15th-order polynomial continuum, and a flat (zero-order) additive continuum. Our model is convolved with an LSF derived from fitting the twilight sky flat frames with a high-resolution Solar spectrum.

# 4. Results

## 4.1. Search Criteria of cEs and Statistical Properties of Selected Sample

To select a clean sample of cE galaxies we cross-matched a catalog generated by SourceXtractor++ with the photometric catalog of DeCALS (Legacy Survey DR10; A. Dey et al. 2019), the spectroscopic redshift catalogs of DESI (DESI Collaboration et al. 2024a, 2024b), SDSS, and Hectospec (as a part of RCSEDv2[^8]), and a full spectroscopic sample of galaxies observed with the Binospec spectrograph (Section 2.3). The Coma cluster sample of cEs in the literature includes nine objects—seven galaxies from J. Price et al. (2009) and two from I. Chilingarian et al. (2009).

<figure><img src="image_4.png" /><figcaption>**Figure 2.** Color–magnitude diagram for all Coma cluster members from DESI DR1, including cE galaxies described in the literature and galaxies from our sample.</figcaption></figure>

### 4.1.1. Photometric Selection

Initially, we applied just the size ($R_e < 1''2 = 0.6$ kpc) and mean effective surface brightness ($\langle\mu_{e,G}\rangle < 22$ mag arcsec⁻²) criteria to our catalog of photometric properties to demonstrate that we can reproduce the sample of Coma cluster cEs from the literature. However, this selection produced a sample heavily contaminated by normal elliptical galaxies at higher redshift with colors indistinguishable from cE with red colors arising from higher metallicity.

We moved to a two-step selection procedure. First, we applied the magnitude ($M_r > -19.5$ mag), shape (ellipticity ($1-b/a$) < 0.25), and color ($0.75 < g - r < 0.9$ mag) selection to the entire SourceXtractor++ catalog cross-matched against integrated photometric measurements from DESI Legacy Surveys catalog (A. Dey et al. 2019). In this first step, we do not apply the surface brightness criterion.

Selection by these three photometric criteria is 89% complete for cE in the literature, yielding 1806 objects, of which 916 have redshifts from DESI or RCSED (SDSS and Hectospec). However, only 22 of the selected galaxies are Coma cluster members. The low 2% purity of the sample, defined as the fraction of objects that pass the selection criteria and have redshifts consistent with the Coma cluster among all objects with redshifts, is due to contamination from background star-forming galaxies at higher redshifts. As shown in the color–magnitude diagram (Figure 2), the cEs in our sample lie above the Coma cluster red sequence, demonstrating that simple color cuts alone cannot reliably select compact ellipticals.

The second step in the photometric selection procedure is to reintroduce the mean effective surface brightness constraint cEs ($\langle\mu_{e,G}\rangle < 22$ mag arcsec⁻²) and the limit on the Sérsic index of the outer component of the light profile ($n > 1.2$). These constraints reduced the number of background objects passing the ($g - r$) color-cut criteria (Figure 3). The completeness and purity of the sample are now 78% and 10%, respectively. Of 210 objects and 132 objects with redshifts, only 13 are Coma cluster members. The purity still remains too low to rely solely on photometric criteria to identify cE galaxies in the Coma cluster.

<footnote>[^8]: https://rcsed2.voxastro.org/</footnote>
<figure><img src="image_5.png" /><figcaption>**Figure 3.** Distribution of redshifts for galaxies that satisfy initial criteria plus $\mu_{e,g}$ and $n$ constraints.</figcaption></figure>

### 4.1.2. Spectroscopic Selection of the Coma Cluster Members

To increase the purity of our sample, we use spectroscopic redshift measurements ($0.01 < z < 0.037$) and galaxy properties derived from full spectral fitting of the DESI EDR spectra. cEs typically are not forming stars and lack emission lines in their spectra. We add the requirement $H\alpha$ nondetection ($F_{H\alpha} < 5 \Delta F_{H\alpha}$) to the photometric size and mean effective surface brightness criteria (Section 4.1.1). With the DESI spectral signal-to-noise ratio per pixel $S/N_{spec} > 2$, this limit is sensitive to star formation activity in last 50 Myr. We did not apply color or Sérsic index cuts because the emission line filter is more effective.

Our final sample, consisting of 13 Coma cluster cEs, is presented in Table 1. Of these, 7 were previously known, while 6 were identified by J. Price et al. (2009) and 1 by I. Chilingarian et al. (2009).

Two galaxies, GMP3511 and GMP3424, were observed with Binospec in the slit masks Coma_dE2a and ComaA. These spectra yield better velocity dispersion and stellar population measurements than the DESI EDR data because they have a much higher signal-to-noise ratio and provide spatially resolved information along the slit.

### 4.2. Photometric Properties of cE Galaxies

We present the photometric properties of our 13 cEs in Table 1 along with information about their hosts. We show the position of our galaxies in the Coma cluster in Figure 1. In all, 8 cEs are in the central region of the Coma cluster, while 5 are located $d_{proj} > 400$ kpc from the cluster center. We place our cE galaxies in structural correlations compiled from the literature in Figure 4. All lie in the cE loci in both diagrams, with an extension toward UCDs.

### 4.3. cE Stellar Populations

We present the cE stellar population properties derived from full DESI EDR spectrum fits in Table 2 and illustrate relations between stellar velocity dispersion, metallicity and absolute magnitude in B band in Figure 5. Eight objects have velocity dispersions typical of cE galaxies, while the other five have lower values, possibly because they have lower stellar mass. Six galaxies have stellar ages from 7 to 13 Gyr, and six have younger ages, 4–7 Gyr, indicating more recent truncation of

star formation. All measured metallicities exceed $[Z/H] > -0.15$ dex.

GMP5500 has a measured age of $\sim 1.3$ Gyr, and its position on the $(g-r)M_r$ diagram places it in the “green valley” (Figure 2). GMP5500’s colors resemble those of more extended diffuse poststarburst galaxies in the Coma cluster (K. A. Grishin et al. 2021) and its spectrum, which cannot be described with either an SSP or a truncated star formation history, which requires a recent starburst. We exclude this galaxy from the discussion in the next sections but leave it on our final cE list.

Our analysis of the GMP3424 velocity profile derived from Binospec spectra (Figure 6) indicates rotation with a semiamplitude of $7 \text{ km s}^{-1}$. The dispersion profile for this galaxy is almost flat at around $35 \text{ km s}^{-1}$ with a central dip of a few $\text{ km s}^{-1}$. The age profile shows a similar central dip, decreasing from 9.0 to 7.5 Gyr. In contrast, GMP3511 does not show any rotation, and its central velocity dispersion reaches $110 \text{ km s}^{-1}$.

## 5. Discussion

### 5.1. cE Formation in Infalling Groups

We identified potential cE host galaxies for our sample, combining spectroscopic and luminosity-based criteria. For each identified cE we searched for galaxies within 300 kpc with luminosity $M_g < -19$ mag and a velocity differing by $<300 \text{ km s}^{-1}$. This velocity difference is the typical velocity dispersion of low-mass galaxy groups of $M_{200} \sim 10^{13} M_{\odot}$ (E. Munari et al. 2013). We validated the list of potential host candidates by visual inspection. We confirmed that all of our cE galaxies with old stellar populations, except one, have hosts. The hosts are both near the center of the Coma cluster and more distant. One cE, cEJ1303+2800, is located only 26 kpc away from a more massive galaxy PGC 93700 but has a velocity difference of $776 \text{ km s}^{-1}$ inconsistent with a gravitationally bound system. This may be the remnant of a galaxy group destroyed by tidal interactions (R. Haggar et al. 2023).

We identified four cEs outside the central region of the cluster ($d_{proj} > 150$ kpc). Because they have massive hosts these may be cEs preprocessed in infalling groups. However, the HSC-g data set does not show any evidence for tidal interactions, including tidal tails, down to $29 \text{ mag arcsec}^{-2}$. The absence of tidal tails suggests that putative stripping events must have occurred more than 2 Gyr ago based on simulations of the persistence of tidal tails (B. Mancillas et al. 2019). In Figure 7 we show these cEs in the Coma cluster’s caustic diagram. Two galaxies from our sample, cEJ1252 +2735 and GMP1993, are located in the typically infalling portion of the caustic diagram, as indicated by a high LOS velocity for their projected radius (C. P. Haines et al. 2015). The other two other galaxies have lower LOS velocities and projected radii, and their orbital history based on the caustic diagram is ambiguous. These could be either infalling, with their true distances from the cluster core masked by projection, or back-splash galaxies.

To estimate the potential contribution of the preprocessing channel we estimate the freefall time of the four outer cEs assuming zero orbital energy and zero orbital angular momentum, i.e., purely radial parabolic orbits. This estimate requires knowledge of the 3D velocity vectors and 3D distances from the center of the cluster. The full freefall
<table><caption>**Table 1**

Photometric Properties of the Selected cEs and Information about the Host Association</caption><thead><tr><th>#</th><th>cE Name</th><th>R.A.<br>J2000</th><th>Decl.<br>J2000</th><th>M<sub>g</sub><br>(mag)</th><th>⟨μ<sub>g</sub>⟩<sub>ε</sub><br>(mag arcsec<sup>-2</sup>)</th><th>R<sub>ε</sub><br>(kpc)</th><th>Host</th><th>d<sub>proj</sub><br>(kpc)</th><th>Δv<br>(km s<sup>-1</sup>)</th><th>d<sub>projCC</sub><br>(kpc)</th></tr></thead><tbody><tr><td>1</td><td>GMP2663</td><td>195.11394</td><td>28.00929</td><td>-14.833 ± 0.004</td><td>21.633 ± 0.012</td><td>0.388 ± 0.002</td><td>NGC 4889</td><td>128.62</td><td>195.40</td><td>347.59</td></tr><tr><td>2</td><td>GMP2777</td><td>195.07869</td><td>28.00932</td><td>-17.241 ± 0.001</td><td>19.854 ± 0.004</td><td>0.518 ± 0.001</td><td>NGC 4889</td><td>84.16</td><td>286.10</td><td>294.76</td></tr><tr><td>3</td><td>CcGV1</td><td>195.19862</td><td>28.09277</td><td>-14.763 ± 0.010</td><td>21.326 ± 0.041</td><td>0.326 ± 0.006</td><td>IC 4045</td><td>7.30</td><td>193.63</td><td>524.48</td></tr><tr><td>4</td><td>GMP3511</td><td>194.84753</td><td>27.91959</td><td>-16.572 ± 0.012</td><td>19.926 ± 0.040</td><td>0.393 ± 0.007</td><td>NGC 4869</td><td>14.01</td><td>228.52</td><td>106.45</td></tr><tr><td>5</td><td>GMP3424<sup>a</sup></td><td>194.87220</td><td>27.94189</td><td>-15.807 ± 0.006</td><td>21.247 ± 0.029</td><td>0.508 ± 0.007</td><td>NGC 4874</td><td>47.93</td><td>1494.84</td><td>51.59</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>NGC 4889</td><td>228.32</td><td>850.33</td><td>...</td></tr><tr><td>6</td><td>GMP3308</td><td>194.90498</td><td>27.97221</td><td>-15.920 ± 0.008</td><td>19.499 ± 0.035</td><td>0.239 ± 0.004</td><td>NGC 4874</td><td>26.62</td><td>426.63</td><td>24.97</td></tr><tr><td>7</td><td>GMP3474</td><td>194.85990</td><td>27.98843</td><td>-15.488 ± 0.018</td><td>21.204 ± 0.065</td><td>0.430 ± 0.012</td><td>NGC 4874</td><td>85.98</td><td>565.10</td><td>79.72</td></tr><tr><td>8</td><td>GMP3027</td><td>194.99960</td><td>27.98940</td><td>-14.084 ± 0.008</td><td>20.927 ± 0.018</td><td>0.198 ± 0.001</td><td>NGC 4889</td><td>53.95</td><td>61.88</td><td>166.37</td></tr><tr><td>9</td><td>CcGV19b</td><td>194.91344</td><td>27.99852</td><td>-13.650 ± 0.075</td><td>20.800 ± 0.196</td><td>0.153 ± 0.013</td><td>NGC 4874</td><td>75.33</td><td>110.93</td><td>73.20</td></tr><tr><td>10</td><td>GMP5500</td><td>194.07849</td><td>27.86737</td><td>-16.069 ± 0.038</td><td>21.311 ± 0.118</td><td>0.591 ± 0.030</td><td>...</td><td>...</td><td>...</td><td>1292.51</td></tr><tr><td>11</td><td>cEJ1252+2735</td><td>193.00710</td><td>27.58707</td><td>-14.426 ± 0.026</td><td>19.489 ± 0.074</td><td>0.120 ± 0.004</td><td>PGC43618</td><td>34.36</td><td>119.90</td><td>3033.23</td></tr><tr><td>12</td><td>cEJ1303+2800<sup>b</sup></td><td>195.87065</td><td>28.01165</td><td>-16.044 ± 0.002</td><td>20.296 ± 0.010</td><td>0.366 ± 0.002</td><td>...</td><td>...</td><td>...</td><td>1521.22</td></tr><tr><td>13</td><td>GMP1993</td><td>195.38512</td><td>27.86547</td><td>-14.902 ± 0.012</td><td>21.886 ± 0.040</td><td>0.450 ± 0.008</td><td>NGC 4921</td><td>44.23</td><td>163.01</td><td>778.17</td></tr></tbody></table>

**Notes.** Column (1): galaxy identifier. Column (2): object name from prioritized list: 1. GMP catalog; 2. J. Price et al. (2009); 3. IAU name. Columns (3)–(4): coordinates of the galaxies. Columns (5)–(6): absolute magnitude and mean surface brightness within the effective radius, effective radius in the g band. Column (7): identified host of the galaxy (for details on the identification technique, see Section 5.1). Column (8): projected distance of the cE from the host galaxy. Column (9): difference between LOS velocity of the cE and potential host. Column (10): projected distance from the cluster center.

<sup>a</sup> For GMP3424 we provide information about possible association with both Coma cluster cEs.

<sup>b</sup> cEJ1303+2800 does not have a potential host with $\Delta v < 300 \text{ km s}^{-1}$ within surrounding $d_{\text{proj}} = 300 \text{ kpc}$. The closest massive galaxy, PGC093700, located 26 kpc away has $\Delta v = 776 \text{ km s}^{-1}$.

velocities are $v_{\text{ff}}(r) = \sqrt{-2\Phi(r)}$, where $\Phi$ is the gravitational potential. The total mass profile of the Coma cluster is close to that of the dark matter mass profile (E. L. Łokas & G. A. Mamon 2003) because the hot intercluster medium and stars contribute less than 10% of the mass at all radii. Thus, we can adopt the analytical potential for a Navarro–Frenk–White (NFW) profile:

$$ \Phi(r) = - \frac{GM_{\text{vir}}}{r} \frac{\ln(1 + r/r_s)}{\ln(1 + c) - c/(1 + c)}, $$

where $r_s = r_{\text{vir}}/c$ is the scale radius, $c = 9.4$ is the concentration parameter, $r_{\text{vir}} = 2.7 \text{ Mpc}$, and $M_{\text{vir}} = 1.2 \cdot 10^{15} M_{\odot}$. We adopt these parameter values as the best fit for the NFW profile in Table 1 of E. L. Łokas & G. A. Mamon (2003). We show the freefall velocity profile in Figure 8.

We estimate the magnitudes of the full velocity ($v_{3D}$) and distance to the cluster center ($r_{3D}$) for a set of possible values of angle between the plane of the sky and velocity vector ($\alpha$). The 3D quantities are related to the observed quantities as

$$ v_{3D} = \frac{v_{\text{los}}}{\cos \alpha}, \quad r_{3D} = \frac{r_{\text{proj}}}{\sin \alpha}, $$

where $v_{\text{los}}$ is the LOS velocity (with respect to the cluster center) and $r_{\text{proj}}$ is the projected distance to the cluster center. The value of $\alpha$ is determined by 3D phase-space values ($r, v_{3D}$) at the intersection.

We estimate the freefall time from energy conservation assuming zero orbital energy and negligible angular momentum:

$$ t_{\text{ff}} = \int_{0}^{r_{0}} \frac{dr}{\sqrt{v_{0}^{2} + 2[\Phi(r_{0}) - \Phi(r)]}}, $$

where $r_0$ is the initial 3D distance and $v_0$ is the initial 3D velocity calculated as described above. We present the calculated freefall times, freefall velocities, and 3D positions in Table 3.

S. Mahajan et al. (2011) studied the dependence of galaxy properties on their velocities and positions in and near the galaxy clusters, using SDSS data and cosmological hydrodynamical simulations (S. Borgani et al. 2004). They plotted the distribution of physical radii versus projected distances for particles in a stacked mock cluster in LOS velocity bins. The galaxies CcGV1 and cEJ1303+2800 have low absolute LOS velocities (within the range [0, $\sigma_{\text{vir}}$], taking $\sigma_{\text{vir}} \sim 1000 \text{ km s}^{-1}$ for the Coma cluster; J. Sohn et al. 2017). The galaxies cEJ1252+2735 and GMP1993 have absolute LOS velocities within $1-2 \sigma_{\text{vir}}$. The projected distance of GMP1993 is $\sim 0.2 R_{\text{vir}}$, and according to Figure 15 in S. Mahajan et al. (2011), the 3D physical distance in such a case remains close to the projected distance. For cEJ1252+2735, located around $1 R_{\text{vir}}$, the physical and projected distances could differ significantly. Therefore, our estimated $R_{3D}$ values agree with Figure 15 in S. Mahajan et al. (2011).

C. P. Haines et al. (2015) suggest that the timescale required for galaxies to reach their first pericenter after being accreted is approximately 0.5–0.8 Gyr based on observations and simulations. They considered a galaxy to be accreted as it crosses $R_{200}$ on infall. Our calculated freefall time for galaxies within $R_{200}$ (excepting galaxy #11) is 0.1–0.4 Gyr. These freefall times are lower because we measured the time from the observed galaxy positions inside $R_{200}$. Our measurements are therefore consistent with the C. P. Haines et al. (2015) pericenter passage times.

For cEJ1252+2735, K. A. Oman & M. J. Hudson (2016) defined infall as the moment when a galaxy passes $2.5 R_{\text{vir}}$ ($R_{\text{vir}} = 2.7 \text{ Mpc}$ for the Coma cluster; E. L. Łokas & G. A. Mamon 2003). It takes $2.5-3.0 \text{ Gyr}$ to reach $R_{\text{vir}}$ and an additional $1.0-1.5 \text{ Gyr}$ to reach the pericenter. The
<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /><figcaption>**Figure 4.** The size–luminosity (J. Kormendy 1977) and the surface brightness–luminosity relations of ETGs and CCSs. cEs from our sample are shown by pink stars. The sources of other galaxies are shown in the legend below the plots. The gray-filled areas and dashed lines denote the parameter space from Section 4.1. References: R. Bender et al. 1992; I. V. Chilingarian 2009; M. Geha et al. 2003; S. de Rijcke et al. 2005; I. V. Chilingarian et al. 2008b; N. F. Martin et al. 2016; M. Yagi et al. 2016; A. W. McConnachie 2012; E. A. Evstigneeva et al. 2007; I. V. Chilingarian et al. 2011; S. G. Djorgovski et al. 1997; P. Martini & L. C. Ho 2004; I. V. Chilingarian & G. A. Mamon 2008.</figcaption></figure>

estimated $R_{3D}$ for cEJ1252+2735 is 3.5 Mpc, placing it between $R_{vir}$ and $2.5R_{vir}$. The estimated freefall time is 1.2 Gyr, including the time required to reach the virial radius and the time to then reach the pericenter. We conclude that all estimated freefall times are consistent with simulations and observations.

É. Tollet et al. (2017) estimate the orbital times of galaxies from their entry into the cluster to their passage

<figure><img src="image_8.png" /><figcaption>**Figure 5.** Relations between stellar velocity dispersion ($\sigma$, top panel), metallicity ([Z/H], bottom panel), and absolute magnitude in the B band ($M_B$) of ETGs and CCSs. cEs from our sample are shown as pink stars. The sources of other galaxy types are indicated in the legend. References: A. W. McConnachie 2012; I. V. Chilingarian et al. 2008b; I. V. Chilingarian et al. 2011.</figcaption></figure>

<table><caption>**Table 2**
Kinematics and Stellar Populations of the cE Sample</caption><thead><tr><th>#</th><th>V<br>(km s<sup>-1</sup>)</th><th>σ<br>(km s<sup>-1</sup>)</th><th>t<sub>SSP</sub><br>(Gyr)</th><th>[Z/H]<br>(dex)</th></tr></thead><tbody><tr><td>1</td><td>6380.4 ± 4.9</td><td>28.2 ± 7.4</td><td>13.09 ± 0.88</td><td>0.11 ± 0.10</td></tr><tr><td>2</td><td>6217.3 ± 2.6</td><td>95.9 ± 2.5</td><td>5.30 ± 0.16</td><td>0.15 ± 0.00</td></tr><tr><td>3</td><td>6765.5 ± 3.8</td><td>20.3 ± 7.3</td><td>10.46 ± 0.61</td><td>0.07 ± 0.08</td></tr><tr><td>4</td><td>6945.7 ± 3.9</td><td>116.0 ± 3.9</td><td>7.20 ± 0.11</td><td>-0.01 ± 0.03</td></tr><tr><td>5</td><td>5650.1 ± 3.2</td><td>38.5 ± 4.2</td><td>4.21 ± 0.19</td><td>-0.03 ± 0.05</td></tr><tr><td>6</td><td>7621.5 ± 3.4</td><td>64.7 ± 3.7</td><td>8.07 ± 0.06</td><td>0.20 ± 0.00</td></tr><tr><td>7</td><td>7746.0 ± 5.0</td><td>51.7 ± 5.9</td><td>4.45 ± 0.21</td><td>-0.14 ± 0.07</td></tr><tr><td>8</td><td>6585.1 ± 8.3</td><td>31.8 ± 11.8</td><td>4.97 ± 0.70</td><td>-0.09 ± 0.15</td></tr><tr><td>9</td><td>7059.5 ± 8.6</td><td>59.3 ± 9.6</td><td>7.50 ± 0.50</td><td>0.13 ± 0.12</td></tr><tr><td>10</td><td>7233.0 ± 6.1</td><td>43.4 ± 8.3</td><td>1.32 ± 0.01</td><td>0.13 ± 0.05</td></tr><tr><td>11</td><td>8141.3 ± 5.3</td><td>23.0 ± 9.1</td><td>4.23 ± 0.37</td><td>-0.02 ± 0.11</td></tr><tr><td>12</td><td>7180.9 ± 4.3</td><td>70.3 ± 4.6</td><td>9.34 ± 0.40</td><td>-0.13 ± 0.06</td></tr><tr><td>13</td><td>5651.2 ± 8.6</td><td>51.2 ± 9.9</td><td>5.31 ± 0.95</td><td>0.14 ± 0.03</td></tr></tbody></table>

Note. The properties were obtained from DESI EDR spectra.

through pericenter based on cosmological simulations with cluster mass growth through filament accretion. For the most probable infall case, with apocentric distance
<figure><img src="image_9.png" /><figcaption>**Figure 6.** Profiles of the velocity (v), velocity dispersion (σ), age, and metallicity for GMP3424 (top) and GMP3511 (bottom) inferred with PEGASE-HR SSP models for masks' 2D spectra in Coma_dE2a and ComaA slit masks (black and green points, respectively). Legend insets contain information about the position angle (PA) of the slit and S/N. Panels with velocity (v) profiles (top) also show bell-shaped profiles of the mean flux extracted from the slit (gray and green lines).</figcaption></figure>

($R_{apo}$) much larger than a virial radius, $R_{apo} \gg R_{vir}$, the orbital times are less than 0.5 Gyr, consistent with our estimates.

<figure><img src="image_10.png" /><figcaption>**Figure 7.** The caustic diagram of the Coma cluster members, along with position of all cE galaxies from our sample (pink stars) and the selected infalling cE galaxies (additionally marked by numbers according to Table 1), shows possible trajectories for varying angular momentum (L). Each trajectory has timestamps. For galaxy CcGV1 (#3), the timestamp is 75 Myr; for galaxy cEJ1252+2735 (#11), it is 500 Myr; and for galaxies cEJ1303+2800 (#12) and GMP1993 (#13), it is 200 Myr. Solid lines represent trajectories at the maximum possible distance, while dotted lines correspond to the minimum possible (projected) distance for a given L.</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>**Figure 8.** An illustration of the estimation of full distances and full velocities. The purple line illustrates the freefall velocity ($v_{ff}$) profile at different full distances from the cluster center (r), while other lines represent possible full distances and velocities according to projected velocity and distance of the galaxies for zero angular momentum case.</figcaption></figure>

We also examined possible effects of nonzero angular momentum by solving the second-order equation of motion:

$$ \frac{d^2\mathbf{r}}{dt^2} = -\frac{GM(r)}{r^3}\mathbf{r}. $$

The initial state includes six parameters: x, y, z, $v_x$, $v_y$, $v_z$, where x and y are the coordinates in the plane of the sky and $v_z$ is the LOS velocity. These parameters are obtained directly from observations. For the case of zero angular momentum, $r_{3D}$ and $v_{3D}$ can be well constrained.
<table><caption>**Table 3**
Projected and Full 3D Velocities ($v_{LOS}$ and $v_{3D}$, Respectively), Distances ($R_{proj}$ and $R_{3D}$, Respectively) and the Freefall Time ($t_{ff}$) under Assumption of Infalling Orbits</caption><thead><tr><th>#</th><th>Name</th><th><i>v</i><sub>LOS</sub><br>(km s<sup>-1</sup>)</th><th><i>R</i><sub>proj</sub><br>(kpc)</th><th><i>v</i><sub>3D</sub><br>(km s<sup>-1</sup>)</th><th><i>R</i><sub>3D</sub><br>(kpc)</th><th><i>t</i><sub>ff</sub><br>(Myr)</th></tr></thead><tbody><tr><td>3</td><td>CcGV1</td><td>-131</td><td>525</td><td>3817</td><td>525</td><td>122</td></tr><tr><td>11</td><td>cEJ1252+2735</td><td>1213</td><td>3033</td><td>2327</td><td>3555</td><td>1204</td></tr><tr><td>12</td><td>cEJ1303+2800</td><td>260</td><td>1521</td><td>2992</td><td>1527</td><td>423</td></tr><tr><td>13</td><td>GMP1993</td><td>-1228</td><td>778</td><td>3482</td><td>832</td><td>206</td></tr></tbody></table>

**Note.** The freefall time is estimated assuming zero orbital energy and zero angular momentum.

We defined a range of possible z values, -10 to +10 Mpc, and calculated $r_{3D}$ and $v_{ff}$ for nonzero angular momentum to identify the possible parameter space for the dimensionless angular momentum $L = |v_{3D} \times r_{3D}|/(v_{3D} r_{3D})$ and the full distance to the cluster center. We also compute all possible values of $v_x$ and $v_y$ for a given $v_{ff}$ and $v_z$. In Figure 9 we plot possible values for $L$ and $R$ given observed $x$, $y$, and $v_z$.

We determine the minimal and maximal possible distances for a given normalized angular momentum value and plot possible corresponding trajectories: dotted lines represent the minimum possible distance and solid lines the maximum distance. The trajectory for each galaxy is calculated over the time needed to reach the pericenter. All outer cEs reach the inner 500 kpc for $L < 0.5$.

These calculations suggest that the population of cE galaxies in the center of the Coma cluster is expected to grow by 10%–30% over the next 0.4 Gyr. Preprocessing in the infalling groups is therefore likely to be a major contributor to the growth of the cE population in the cluster center.

## 5.2. Origin of the cE Population in the Coma Cluster Center

Using a source catalog based on deep HSC-g images for the Coma cluster we have identified a bimodal population of cE galaxies: a dominant population of cEs in the cluster center and a subpopulation of cEs distributed in the outer parts of the cluster. All of the catalog galaxies outside the cluster center, except one, are hosted by more massive galaxies. This observation is consistent with cE preprocessing in groups, predominantly tidal stripping. We conclude that if cEs initially form in infalling groups, these groups will be destroyed by tidal interactions with the gravitational potential of individual galaxies and the cluster leaving the infalling cEs to contribute to the cE population in the cluster center. The visual inspection of the HST imaging data for cEs in our sample does not reveal prominent host globular cluster (GC) systems, which can be identified as overdensities of the point-source objects around them (Figure 13 in the Appendix). A more detailed quantitative assessment of the globular cluster population in the HST footprint would provide additional support for this scenario but goes beyond the scope of this paper and will be addressed in future work.

Our estimate suggests that preprocessing in groups will contribute up to 30% to the growth of the cE population over the next 0.4 Gyr. An extrapolation of this growth rate to the past and future supports our conclusion that the majority of the central cE population was formed through this channel. This estimate assumes that the cEs we observe in the outer part of the cluster have zero orbital energy and low angular momentum. Because two cE groups are located the phase-space populated mostly by

<figure><img src="image_12.png" /><figcaption>**Figure 9.** Possible values (filled) of dimensionless angular momentum ($L$) and total distance to the cluster center ($r$) for the four cEs in outer parts of the cluster.</figcaption></figure>

the infalling galaxies, we conclude that our assumptions are plausible. Hydrodynamical simulations show that the vast majority of infalling groups do not survive their first passage in the cluster and become unbound after 0.5–1 Gyr after entering the cluster (R. Haggar et al. 2023). Therefore, the cE hosting groups are likely to become unbound well before the accretion of cEs by their host galaxies.

## Acknowledgments

A.S. acknowledges the Russian Science Foundation (RSCF) grant No. 23-12-00146. K.G. acknowledges support from ANR-24-CE31-2896. IC’s research is supported by the Telescope Data Center at the Smithsonian Astrophysical Observatory and by the Smithsonian Institution FY24 combined call grant.

## Appendix
Measurements of Effective Radii

We compare our effective radius measurements with the published catalog based on the decomposition of high-resolution HST images with the GALFIT (C. Y. Peng et al. 2010) code. For this comparison, we choose Coma cluster members with SourceXtractor++ half-light radii larger than their $3\sigma$ uncertainties ($R_e > 3\sigma (R_e)$). In Figure 10 we plot the differences $((R_e - R_e_{lit})/R_e_{lit})$ between the SourceXtractor++ and GALFIT-based $R_e$ measurements. SourceXtractor++ $R_e$ estimates tend to be systematically higher than GALFIT’s. The median relative difference (bias, $\Delta R/R$) is 0.13 with a dispersion of 1.16. A possible explanation of this discrepancy is the difference between the fitting models. We fit galaxies with two- or even three-component models, while C. Hoyos et al. (2011) use a single Sérsic profile. For cE galaxies, the two-component model is superior to a single-component model because most galaxies from the comparison sample contain embedded structures or nuclei. A second contributor to the discrepancy may be the use of different photometric bands. C. Hoyos et al. (2011) analyzed F814W images (I band), while we used g-band data: radial color gradients often observed in ETGs (bluer outer regions compared to centers) will naturally explain larger $R_e$ values in a bluer band.
<figure><img src="image_13.png" /><figcaption>**Figure 10.** Measurements of $R_e$ with SourceXtractor++ applied to HSC-g images compared to the literature GALFIT measurements on HST data from C. Hoyos et al. (2011) and J. Price et al. (2009), along with a histogram of the relative differences between measurements.</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>**Figure 11.** Velocity dispersion measurements of DESI compared to RCSED1 (SDSS sample; I. V. Chilingarian et al. 2017) and DEIMOS (E. Kourkchi et al. 2012) measurements, along with histograms of the relative difference.</figcaption></figure>

Figure 11 compares DESI velocity dispersion measurements with those from the RCSED1 (SDSS sample; I. V. Chilingarian et al. 2017) and DEIMOS (E. Kourkchi et al. 2012) datasets, demonstrating the consistency of the DESI measurements.

Figure 12 displays DESI spectra of cEs with their best-fitting stellar population models, flux uncertainties, and

residuals, illustrating the data quality and accuracy of the spectral fitting used in this work.

Figure 13 shows the 15" × 15" HST F814W cutouts for 10 cE galaxies in our sample. No unambiguous globular cluster systems are apparent around these galaxies. A detailed quantitative assessment of GC populations in the HST footprint is beyond the scope of this work.
<figure><img src="image_15.png" /><figcaption>**Figure 12.** DESI spectra of cEs optimally extracted along the slit flux calibrated in $F_\lambda$ units (black). Their best-fitting stellar population models (red), flux uncertainties (pink), and fitting residuals (gray). Galaxy names from Table 1 are shown in each panel. All data and best-fitting models are smoothed with the Savitzky–Golay filter for display purposes. The right panel illustrates the fit to the calcium triplet region.</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>**Figure 13.** The 15" × 15" HST F814W cutouts for 10 cE galaxies in our sample do not display unambiguous globular cluster systems around them.</figcaption></figure>
ORCID iDs

Aleksandra V. Sharonova https://orcid.org/0009-0007-2825-8758

Kirill A. Grishin https://orcid.org/0000-0003-3255-7340

Igor V. Chilingarian https://orcid.org/0000-0002-7924-3253

Gary A. Mamon https://orcid.org/0000-0001-8956-5953

Nelson Caldwell https://orcid.org/0000-0003-2352-3202

Daniel Fabricant https://orcid.org/0000-0002-1311-4942

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