bluuebunny/crossref_metadata_2025_split huggingface dataset:
Celestial reference frames at multiple radio wavelengths
Authors: Jacobs C. S. 
Published: March 2015

AbstractIn 1997 the IAU adopted the International Celestial Reference Frame (ICRF) built from S/X VLBI data. In response to IAU resolutions encouraging the extension of the ICRF to additional frequency bands, VLBI frames have been made at 24, 32, and 43 GHz. Meanwhile, the 8.4 GHz work has been greatly improved with the 2009 release of the ICRF-2. This paper discusses the motivations for extending the ICRF to these higher frequency radio bands. Results to date will be summarized including evidence that the high frequency frames are rapidly approaching the accuracy of the 8.4 GHz ICRF-2. We discuss current limiting errors and prospects for the future accuracy of radio reference frames. We note that comparison of multiple radio frames is characterizing the frequency dependent systematic noise floor from extended source morphology and core shift. Finally, given Gaia's potential for high accuracy optical astrometry, we have simulated the precision of a radio-optical frame tie to be ~10–15 μas (1-σ, per component).
EPM — High-Precision Planetary Ephemerides of IAA RAS for Scientific Research and Astronavigation on the Earth and in Space
Authors: Pitjeva E. V. 
Published: March 2015

AbstractThe last version of the planet part of EPM's ephemerides of IAA RAS (EPM2011) is described briefly. At present EPM ephemerides are the basis for the Russian Astronomical and Nautical Astronomical Yearbooks and are used for scientific research.
The IERS Conventions (2010): reference systems and new models
Authors: Luzum B. , Petit G. 
Published: March 2015

AbstractThe IERS Conventions (2010) provides the international standard for models for use in the generation of celestial reference systems (CRS), terrestrial reference systems (TRS), and the Earth orientation parameters (EOPs) that relate the associated frames. Significant improvements over the previous IERS Conventions (2003) are outlined, and an overview of the latest adopted models and standards is shown. Finally, future plans for the Conventions are provided.
Seeking footprints of the primeval Universe in dwarf galaxies
Authors: Hidalgo Sebastian L. ,   the LCID group
Published: March 2015

AbstractWe present the star formation histories (SFHs) of four isolated dwarf galaxies, Cetus, Tucana, LGS-3, and Phoenix, as a function of galactocentric radius. Our results suggest that beyond some distance from the center, there are no significative differences in fundamental properties of these galaxies, such as the star formation rate (SFR) or age-metallicity relation (AMR). The stellar content of this region would be composed of old (≳ 10.5 Gyr) metal-poor stars only. In the innermost regions, dwarf galaxies appear to have formed stars during time intervals which duration varies from galaxy to galaxy. This extended star formation produces the dichotomy between dwarf spheroidal (dSph) and dwarf Transition (dTr) galaxy types.
The Chemical Evolution of Milky Way Satellite Galaxies from Keck Spectroscopy
Authors: Kirby Evan N. 
Published: March 2015

AbstractThe primary data product of a recent Keck/DEIMOS spectroscopic campaign of eight Milky Way dwarf spheroidal (dSph) satellite galaxies is a catalog of nearly 3000 red giants with spectral synthesis-based abundance measurements of Fe and the α elements Mg, Si, Ca, and Ti. The dSph metallicity distributions show that the histories of the less luminous dSphs were marked by massive amounts of metal loss. The [α/Fe] distributions reveal that the early star formation histories (at a lookback time of >12 Gyr) of most dSphs were very similar and that Type Ia supernova ejecta contributed to the abundances of all but the most metal-poor ([Fe/H] < −2.5) stars. This large data set allows inferences of past outflows from the dSphs in order to determine their contribution to the metal content of the intergalactic medium.
CN Anomalies in the Halo System
Authors: Carollo Daniela 
Published: March 2015

AbstractI present an evaluation of the kinematic properties of halo red giants thought to have formed in globular clusters based on the strength of their UV/blue CN and CH absorption features. The sample has been selected from the catalog of Martell et al. (2011). The orbital parameters of CN-strong halo stars are compared to those of the inner and outer halo populations, and to the orbital parameters of globular clusters with well-studied Galactic orbits. It has been found that both the clusters and the CN-strong field stars exhibit kinematic and orbital properties similar to the inner halo population, indicating that globular clusters could be a significant source of inner halo field stars, and suggesting that both globular clusters and CN-strong stars could belong primarily to the inner halo population of the Milky Way.
Origin of structures in disc galaxies: internal or external processes?
Authors: Athanassoula E. 
Published: March 2015

AbstractDisc galaxies have a number of structures, such as bars, spirals, rings, discy bulges, m = 1 asymmetries, thick discs, warps etc. I will summarise what is known about their origin and in particular whether it is due to an external or an internal process. The former include interactions, major or minor mergers etc, while the latter include instabilities, or driving by another component of the same galaxy, as e.g. the bar or the halo. In cases where more than one process is eligible, I will analyse whether it is possible to distinguish between different origins, and what it would take to do so. This discussion will show that, at least in some cases, it is difficult to distinguish between an internal and an external origin.
Rotation of classical bulges during secular evolution of barred galaxies
Authors: Saha Kanak , Gerhard Ortwin 
Published: March 2015

AbstractBar driven secular evolution plays a key role in changing the morphology and kinematics of disk galaxies, leading to the formation of rapidly rotating boxy/peanut bulges. If these disk galaxies also hosted a preexisting classical bulge, how would the secular evolution influence the classical bulge, and also the observational properties.We first study the co-evolution of a bar and a preexisting non-rotating low-mass classical bulge such as might be present in galaxies like the Milky Way. It is shown with N-body simulations that during the secular evolution, such a bulge can gain significant angular momentum emitted by the bar through resonant and stochastic orbits. Thereby it transforms into a cylindrically rotating, anisotropic and triaxial object, embedded in the fast rotating boxy bulge that forms via disk instability (Saha et al. 2012). The composite boxy/peanut bulge also rotates cylindrically.We then show that the growth of the bar depends only slightly on the rotation properties of the preexisting classical bulge. For the initially rotating small classical bulge, cylindrical rotation in the resulting composite boxy/peanut bulge extends to lower heights (Saha & Gerhard 2013). More massive classical bulges also gain angular momentum emitted by the bar, inducing surprisingly large rotational support within about 4 Gyrs (Saha et al. in prep).
Comparison of NIRS0S Ks-band and S4G 3.6 micron data: Fourier amplitudes, force profiles and color maps
Authors: Salo Heikki , Laurikainen Eija ,   the S4G Collaboration
Published: March 2015

AbstractNear-IR observations are considered to give an extinction-free view of the old stellar population in galaxies, thus ideal for the analysis of gravitational torques associated with bar and spiral structures. In the past, H or Ks band data have often been employed (Buta et al. 2010, Salo et al. 2010). S4G (Spitzer Survey of Stellar Structure in Galaxies, Sheth et al. 2010) provides new deep homogenious 3.6 and 4.5 micron data for over 2000 nearby galaxies, allowing to probe the bar and spiral properties over a wide range of morphological types and environments. Here we compare the Fourier-amplitude profiles derived from S4G data for about 50 early-type disk galaxies (SO and S0/a), with those from NIRSOS Ks data (Near-IR S0 Survey, Laurikainen et al. 2011). We also make detailed Ks-3.6 micron color maps. Interestingly, nuclear ring features stand up very clearly in these maps, indicating significantly different contributions of recent star formation in the Ks and 3.6 micron bands. However, the effect of these detailed differences on the overall force profiles is fairly small: this confirms that the S4G data can be confidently used for estimation of bar torques.
Stellar populations in bulges and disks and the secular evolution connection
Authors: Peletier Reynier 
Published: March 2015

AbstractIn recent years a considerable amount of new data has become available about stellar populations in the central regions of galaxies. I will discuss what stellar populations can tell us about the formation origin of bulges, and how this relates to the formation of the central regions in giant and dwarf ellipticals. In particular I will concentrate on results from integral field spectroscopy and Spitzer imaging at 3.6, 4.5 and 8 microns.
The growth of mass and metallicity in bulges and disks: CALIFA perspective
Authors: González Delgado R. M. , Pérez E. , Cid Fernandes R. , García-Benito R. , de Amorim A. , Sánchez S. F. , Husemann B. , Fernández R. López , Cortijo C. , Lacerda E. , Mast D. ,   the CALIFA collaboration
Published: March 2015

AbstractCALIFA (Calar Alto Legacy Integral Field Area) is a 3D spectroscopic survey of 600 nearby galaxies that we are obtaining with PPaK@3.5m at Calar Alto (Sánchez et al. 2012; Husemann et al. 2012). This pioneer survey is providing valuable clues on how the mass and metallicity grow in the different galactic spatial sub-components (“bulge” and “disk”). Processed through spectral synthesis techniques, CALIFA datacubes allow us to, for the first time, spatially resolve the star formation history of galaxies (Cid Fernandes et al. 2012). The richness of this approach is already evident from the results obtained for the first ~ 100 galaxies of the sample (Pérez et al. 2012). We have found that galaxies grow inside-out, and that the growth rate depends on a galaxy's mass. Here, we present the radial variations of physical properties sorting galaxies by their morphological type (Figure 1). We have found a good correlation between the stellar mass surface density, stellar ages and metallicities and the Hubble type, but being the the early type spirals (Sa-Sbc) the galaxies with strong negative age and metallicity gradient from the bulge to the disk.
Stellar populations of bulges in galaxies with a low surface-brightness disc
Authors: Morelli L. , Corsini E. M. , Pizzella A. , Dalla Bontà E. , Coccato L. , Méndez-Abreu J. , Cesetti M. 
Published: March 2015

AbstractThe radial profiles of the Hβ, Mg, and Fe line-strength indices are presented for a sample of eight spiral galaxies with a low surface-brightness stellar disc and a bulge. The correlations between the central values of the line-strength indices and velocity dispersion are consistent to those known for early-type galaxies and bulges of high surface-brightness galaxies. The age, metallicity, and α/Fe enhancement of the stellar populations in the bulge-dominated region are obtained using stellar population models with variable element abundance ratios. Almost all the sample bulges are characterized by a young stellar population, on-going star formation, and a solar α/Fe enhancement. Their metallicity spans from high to sub-solar values. No significant gradient in age and α/Fe enhancement is measured, whereas only in a few cases a negative metallicity gradient is found. These properties suggest that a pure dissipative collapse is not able to explain formation of all the sample bulges and that other phenomena, like mergers or acquisition events, need to be invoked. Such a picture is also supported by the lack of a correlation between the central value and gradient of the metallicity in bulges with very low metallicity. The stellar populations of the bulges hosted by low surface-brightness discs share many properties with those of high surface-brightness galaxies. Therefore, they are likely to have common formation scenarios and evolution histories. A strong interplay between bulges and discs is ruled out by the fact that in spite of being hosted by discs with extremely different properties, the bulges of low and high surface-brightness discs are remarkably similar.
Evolution of the star formation efficiency in galaxies
Authors: Braine Jonathan 
Published: March 2015

AbstractThe physical and chemical evolution of galaxies is intimately linked to star formation, We present evidence that molecular gas (H2) is transformed into stars more quickly in smaller and/or subsolar metallicity galaxies than in large spirals – which we consider to be equivalent to a star formation efficiency (SFE). In particular, we show that this is not due to uncertainties in the N(H2)/Ico conversion factor. Several possible reasons for the high SFE in galaxies like the nearby M33 or NGC 6822 are proposed which, separately or together, are the likely cause of the high SFE in this environment. We then try to estimate how much this could contribute to the increase in cosmic star formation rate density from z = 0 to z = 1.
Tidal evolution of dwarf galaxies with shallow dark matter density profiles
Authors: Łokas Ewa L. 
Published: March 2015

AbstractOne of the scenarios for the formation of dwarf spheroidal galaxies in the Local Group proposes that the objects formed from late type dwarfs via tidal interaction with bigger galaxies such as the Milky Way and Andromeda. The scenario naturally explains the morphology-density relation observed for dwarf galaxies in the Local Group. Using N-body simulations we study the long-term tidal evolution of dwarf galaxies in the vicinity of the Milky Way. The dwarf galaxies were initially composed of stellar disks embedded in dark matter haloes of different inner density slopes including shallow ones recently obtained in N-body+hydro simulations of dwarf galaxy formation in isolation. Such progenitors were placed on five different orbits around the Milky Way and their evolution was followed for 10 Gyr. The outcome of the evolution, in terms of the mass loss, morphological transformation and randomization of stellar orbits depends very sensitively on the inner density slope of dark matter. The effects of tides are stronger for dwarfs with shallower slopes; they are more heavily stripped, in some cases down to the scale of ultra-faint satellites of the Milky Way or even dissolved completely with obvious implications for the missing satellites problem. The morphological evolution of the stellar component, from rotationally supported disks to spheroids dominated by random motions, also proceeds faster. In addition, bars which usually form at the first pericenter passage are created more easily and live longer in dwarfs with shallow dark matter density profiles on extended orbits.
A new model for the Milky Way bar
Authors: Wang Yougang , Zhao Hongsheng , Mao Shude , Rich R. M. 
Published: March 2015

AbstractWe use Schwarzschild's orbit-superposition technique to construct self-consistent models of the Galactic bar. Using χ2 minimisation, we find that the best-fit Galactic bar model has a pattern speed Ωp=60 km s−1 kpc−1, disk mass Md=1.0×1011M⊙ and bar angle θbar=20° for an adopted bar mass Mbar=2×1010M⊙. The model can reproduce not only the three-dimensional and projected density distributions but also velocity and velocity dispersion data from the BRAVA survey. We also predict the proper motions in the range l=[−12°,12°], b=[−10°,10°], which appear to be higher than observations in the longitudinal direction. The model is stable within a timescale of 0.5 Gyr, but appears to deviate from steady-state on longer timescales. Our model can be further tested by future observations such as those from GAIA.
A secularly evolved model for the Milky Way bar and bulge
Authors: Martinez-Valpuesta Inma , Gerhard Ortwin 
Published: March 2015

AbstractBars are strong drivers of secular evolution in disk galaxies. Bars themselves can evolve secularly through angular momentum transport, producing different boxy/peanut and X-shaped bulges. Our Milky Way is an example of a barred galaxy with a boxy bulge. We present a self-consistent N-body simulation of a barred galaxy which matches remarkably well the structure of the inner Milky Way deduced from star counts. In particular, features taken as signatures of a second “long bar“ can be explained by the interaction between the bar and the spiral arms of the galaxy (Martinez-Valpuesta & Gerhard 2011). Furthermore the structural change in the bulge inside l = 4° measured recently from VVV data can be explained by the high-density near-axisymmetric part of the inner boxy bulge (Gerhard & Martinez-Valpuesta 2012). We also compare this model with kinematic data from recent spectroscopic surveys. We use a modified version of the NMAGIC code (de Lorenzi et al. 2007) to study the properties of the Milky Way bar, obtaining an upper limit for the pattern speed of ~ 42 km/sec/kpc. See Fig. 1 for a comparison of one of our best models with BRAVA data (Kunder et al. 2012).
Searching for observational evidence of radial mixing in the Milky Way disk
Authors: Haywood Misha 
Published: March 2015

AbstractSecular evolution in disks through angular momentum redistribution of stars induce radial mixing of their orbits. While theoretical studies and simulations now abound on the subject - with various predicted effects: disks growth, flattening of metallicity gradients, possible reversing of the mean age as a function of radius in disk, etc, observational evidences remain sparse. In the Galaxy, possible signatures are searched for in the local distributions of velocities, abundances and ages, or in the variation of large scale chemical gradients with time. I will present the current state of affairs and discuss what kind of evidences is available from data in the Milky Way.
How well can we identify pseudobulges?
Authors: Graham Alister 
Published: March 2015

AbstractSince the discovery of rotating galaxy bulges (e.g. Pease 1918; Babcock 1938, 1939), especially in the 1970s (e.g. Rubin, Ford & Kumar 1973; Pellet 1976; Bertola & Capaccioli 1977; Peterson 1978; Mebold et al. 1979; Kormendy & Illingworth 1979), coupled with early computer simulations of disks which formed rotating, exponential-like “pseudobulges” (e.g. Bardeen 1975; Hohl 1975, and references therein), a number of often over-looked problems pertaining to the identification of real “pseudobulges” have arisen. Drawing on my recent review article of disk galaxy structure and modern scaling laws (Graham 2012), some of these important issues are presented. Topics include: classical spheroids with exponential light distributions; curved but continuous scaling relations involving the ‘effective’ structural parameters; the old age of most bulge stars (e.g. Thomas & Davies 2006; MacArthur et al. 2009); that most disk galaxies have bulge-to-disk flux ratios < 1/3 (Graham & Worley 2008); rotation in simulated merger remnants (e.g. Bekki 2010; Keselman & Nusser 2012) plus many other frustrating yet interesting reasons why rotation may not be a definitive signature of bulges built via secular processes (e.g. Babusiaux et al. 2010; Williams et al. 2010, Qu et al. 2011; Saha et al. 2012)
Bar-driven evolution of fast rotators: the role and fate of bars in early and late-type galaxies
Authors: Emsellem Eric , Florent Renaud 
Published: March 2015

AbstractWe have performed state-of-the-art high resolution simulations of early-type galaxies with bars, including (multi-phase) gas, star formation and feedback. The aim of this programme is to better understand the observed morphology, kinematical structures, (2D) metallicity distribution, observed in fast rotators with bars. Our simulations were designed via a newly developed code allowing us to build a library of initial conditions closely mimicking barred galaxies in the Atlas3D sample. We will present the role and importance of bars on the gas fueling, redistribution of angular momentum, and overall secular evolution of fast rotators. These results are compared with actual observations (IFU, CO maps, stellar population distributions) obtained in the course of the Atlas3D project. The results from these “early-type“ simulations will also be compared in the context of recently conducted simulations of later-type barred galaxies, including one of a Milky-Way type object with a resolution down to 0.05 parsec.
Dissecting early-type dwarf galaxies into their multiple components
Authors: Janz Joachim , Laurikainen Eija , Lisker Thorsten , Salo Heikki 
Published: March 2015

AbstractEarly-type dwarf galaxies are often thought to be either more diffuse versions of giant ellipticals or to be low-mass disk galaxies that were quenched and heated by the environment. In both cases, the picture that most astronomers have in mind probably is that of a dynamically hot, regular shaped galaxy, in which any previous substructure has either been smeared out, or has never been there. However, the early-type dwarfs are not that simple.We analyzed ~100 such objects in the Virgo cluster using deep near-infrared images and found that the majority has a multi-component structure, sometimes even with bars or lenses. The study was done by applying GALFIT to images from the SMAKCED collaboration (Stellar content, MAss and K inematics of Cluster Early-type Dwarfs, http://www.smakced.net). The sample comprises early-type galaxies in the Virgo cluster in a brightness range of −19 ≤ Mr ≤ −16 mag, and the data is complete down to Mr=−16.73 mag. The images typically reach a signal-to-noise ratio of 1 per pixel of ~0.25” at a surface brightness of ~22.5 mag/arcsec2 in the H-band. The galaxies were fitted with two-dimensional models, either with a simple Sérsic model or inner and outer components, as well as bars and lenses. Only a fraction of 31% of the galaxies can be fitted with a single Sérsic function. This fraction of “simple“ galaxies turns out to be a strong function of luminosity, with a smaller fraction for brighter objects. The bar fraction is 14% and also in 14% of the galaxies lenses were fitted.When comparing the flattening distribution, the early-type dwarfs are more similar to spiral galaxies than to elliptical or lenticular galaxies. It is disputable whether or not the dwarfs follow a common relation with the bright elliptical galaxies, e.g. in the brightness versus size diagram. At the same time, they appear as smooth continuation of bright late-type galaxies in this diagram. The inner and outer components, as well as the simple galaxies have similar flattening distributions. The inner components are mostly fitted with Sérsic-n values close to~1, i.e. with nearly exponential profiles. We argue that the inner components in the early-type dwarfs are not be bulges but may form parts of the disks, in which the matter was re-distributed during the transformation process from a late-type progenitor.