The HST/ACS Coma Cluster Survey - VII. Structure and assembly of massive galaxies in the centre of the Coma cluster (original) (raw)
Related papers
2013
We constrain the assembly history of galaxies in the projected central 0.5 Mpc of the Coma cluster by performing structural decomposition on 69 massive (M_star >= 10^9 M_sun) galaxies using high-resolution F814W images from the HST Treasury Survey of Coma. Each galaxy is modeled with up to three Sersic components having a free Sersic index n. After excluding the two cDs in the projected central 0.5 Mpc of Coma, 57% of the galactic stellar mass in the projected central 0.5 Mpc of Coma resides in classical bulges/ellipticals while 43% resides in cold disk-dominated structures. Most of the stellar mass in Coma may have been assembled through major (and possibly minor) mergers. Hubble types are assigned based on the decompositions, and we find a strong morphology-density relation; the ratio of (E+S0):spirals is (91.0%):9.0%. In agreement with earlier work, the size of outer disks in Coma S0s/spirals is smaller compared with lower-density environments captured with SDSS (Data Release 2). Among similar-mass clusters from a hierarchical semi-analytic model, no single cluster can simultaneously match all the global properties of the Coma cluster. The model strongly overpredicts the mass of cold gas and underpredicts the mean fraction of stellar mass locked in hot components over a wide range of galaxy masses. We suggest that these disagreements with the model result from missing cluster physics (e.g., ram-pressure stripping), and certain bulge assembly modes (e.g., mergers of clumps). Overall, our study of Coma underscores that galaxy evolution is not solely a function of stellar mass, but also of environment.
Environmental Effects in the Structural Parameters of Galaxies in the Coma Cluster
Astronomical Journal, 2004
We have studied 116 bright galaxies from the Coma Cluster brighter than mr=17 mag. From a quantitative morphological analysis we find that the scales of the disks are smaller than those of field spiral galaxies. There is a correlation between the scale of the disks and the position of the galaxy in the cluster; no large disks are present near the center of the cluster or in high-density environments. The structural parameters of the bulges are not affected by the environment. We have analyzed the distribution of blue and red objects in the cluster. For spirals there is a trend between color and position in the cluster. The bluest spiral galaxies are located at larger projected radii; they also show larger velocity dispersions than the red ones. The differences in the scale of the disks between cluster galaxies and local samples of isolated galaxies and the color distribution of the objects can be understood in terms of the harassment scenario.
The fundamental properties of early-type galaxies in the Coma Cluster
2001
We report the results of a high quality spectral study of early-type galaxies within the Coma Cluster core. Stellar population analysis using Lick/IDS indices to break the age/metallicity degeneracy are presented, probing their formation history and properties. A clear metallicity trend and a dominant single age population are found.
Quantitative Morphology of Galaxies in the Core of the Coma Cluster
Astrophysical Journal, 2004
We present a quantitative morphological analysis of 187 galaxies in a region covering the central 0.28 square degrees of the Coma cluster. Structural parameters from the best-fitting Sersic r^{1/n} bulge plus, where appropriate, exponential disc model, are tabulated here. This sample is complete down to a magnitude of R=17 mag. By examining the Edwards et al. (2002) compilation of galaxy redshifts in the direction of Coma, we find that 163 of the 187 galaxies are Coma cluster members, and the rest are foreground and background objects. For the Coma cluster members, we have studied differences in the structural and kinematic properties between early- and late-type galaxies, and between the dwarf and giant galaxies. Analysis of the elliptical galaxies reveals correlations among the structural parameters similar to those previously found in the Virgo and Fornax clusters. Comparing the structural properties of the Coma cluster disc galaxies with disc galaxies in the field, we find evidence for an environmental dependence: the scale lengths of the disc galaxies in Coma are 30% smaller. A kinematical analysis shows marginal differences between the velocity distributions of ellipticals with Sersic index n<2 (dwarfs) and those with n>2 (giants); the dwarf galaxies having a greater (cluster) velocity dispersion. Finally, our analysis of all 421 background galaxies reveals a non-uniform distribution in redshift with contrasts in density ~3, characterized by a void extending from ~10,000 to ~20,000 km s^{-1}, and two dense and extended structures centred at ~20,000 and ~47,000 km s^{-1}.
Which Galaxies Host Bars and Disks? A Study of the Coma Cluster
The Astrophysical Journal, 2010
We present a study of the bar fraction in the Coma cluster galaxies based on a sample of ∼ 190 galaxies selected from the Sloan Digital Sky Survey Data Release 6 (SDSS-DR6) and observed with the Hubble Space Telescope (HST) Advanced Camera for Survey (ACS). The unprecedented resolution of the HST-ACS images allow us to explore the presence of bars, detected by visual classification, throughout a luminosity range of 9 magnitudes (−23 M r −14), permitting us to study the poor known region of dwarf galaxies. We find that bars are hosted by galaxies in a tight range of both luminosities (−22 M r −17) and masses (10 9 M * /M ⊙ 10 11). This result holds when comparing with a sample of bright/massive field galaxies. In addition, we find that the bar fraction does not vary significantly when going from the center to the cluster outskirts, implying that cluster environment plays a second order role in bar formation/evolution. The shape of the bar fraction distribution with respect to both luminosity and mass is well matched by the luminosity distribution of disk galaxies in Coma, indicating that bars are good tracers of cold stellar disks. We discuss the implications of our results for the formation and evolution scenarios of bars and disks.
The HST /ACS Coma Cluster Survey - V. Compact stellar systems in the Coma Cluster
Monthly Notices of the Royal Astronomical Society, 2009
The HST ACS Coma Cluster Treasury Survey is a deep two passband imaging survey of the nearest very rich cluster of galaxies, covering a range of galaxy density environments. The imaging is complemented by a recent wide field redshift survey of the cluster conducted with Hectospec on the 6.5m MMT. Among the many scientific applications for this data are the search for compact galaxies. In this paper, we present the discovery of seven compact (but quite luminous) stellar systems, ranging from M32-like galaxies down to ultra-compact dwarfs (UCDs)/dwarf to globular transition objects (DGTOs).
The HST/ACS Coma Cluster Survey - III. Structural parameters of galaxies using single Sérsic fits★
Monthly Notices of the Royal Astronomical Society, 2011
We present a catalogue of structural parameters for 8814 galaxies in the 25 fields of the HST/ACS Coma Treasury Survey. Parameters from Sérsic fits to the two-dimensional surface brightness distributions are given for all galaxies from our published Coma photometric catalogue with mean effective surface brightness brighter than 26.0 mag arcsec −2 and brighter than 24.5 mag (equivalent to absolute magnitude -10.5), as given by the fits, all in F814W(AB). The sample comprises a mixture of Coma members and background objects; 424 galaxies have redshifts and of these 163 are confirmed members. The fits were carried out using both the GIM2D and GALFIT codes. We provide the following parameters: Galaxy ID, RA, DEC, the total corrected automatic magnitude from the photometric catalogue, the total magnitude of the model (F814W AB ), the geometric mean effective radius R e , the mean surface brightness within the effective radius µ e , the Sérsic index n, the ellipticity and the source position angle. The selection limits of the catalogue and the errors listed for the Sérsic parameters come from extensive simulations of the fitting process using synthetic galaxy models. The agreement between GIM2D and GALFIT parameters is sensitive to details of the fitting procedure; for the settings employed here the agreement is excellent over the range of parameters covered in the catalogue. We define and present two goodness-of-fit indices which quantify the degree to which the image can be approximated by a Sérsic model with concentric, coaxial elliptical isophotes; such indices may be used to objectively select galaxies with more complex structures such as bulge-disk, bars or nuclear components.
The Astrophysical …, 2011
Intracluster stellar populations are a natural result of tidal interactions in galaxy clusters. Measuring these populations is difficult, but important for understanding the assembly of the most massive galaxies. The Coma cluster of galaxies is one of the nearest truly massive galaxy clusters, and is host to a correspondingly large system of globular clusters (GCs). We use imaging from the HST/ACS Coma Cluster Survey to present the first definitive detection of a large population of intracluster GCs (IGCs) that fills the Coma cluster core and is not associated with individual galaxies. The GC surface density profile around the central massive elliptical galaxy, NGC 4874, is dominated at large radii by a population of IGCs that extend to the limit of our data (R < 520 kpc). We estimate that there are 47000 ± 1600 (random) +4000
Monthly Notices of the Royal Astronomical Society: Letters, 2010
We study the stellar population far into the halo of one of the two brightest galaxies in the Coma cluster, NGC 4889, based on deep medium resolution spectroscopy with FOCAS at the Subaru 8.2m telescope. We fit single stellar population models to the measured line-strength (Lick) indices (Hβ, Mgb, [MgFe]' and ). Combining with literature data, we construct radial profiles of metallicity, [α/Fe] element abundance ratio and age for NGC 4889, from the center out to ∼ 60 kpc (∼ 4R e ). We find evidence for different chemical and star formation histories for stars inside and outside 1.2R e = 18 kpc radius. The inner regions are characterized by a steep [Z/H] gradient and high [α/Fe] at ∼2.5 times solar value. In the halo, between 18 and 60 kpc, the [Z/H] is near-solar with a shallow gradient, while [α/Fe] shows a strong negative gradient, reaching solar values at 60 kpc. We interpret these data in terms of different formation histories for both components. The data for the inner galaxy are consistent with a rapid, quasi-monolithic, dissipative merger origin at early redshifts, followed by one or at most a few dry mergers. Those for the halo argue for later accretion of stars from old systems with more extended star formation histories. The half-light radius of the inner component alone is estimated as ∼ 6 kpc, suggesting a significantly smaller size of this galaxy in the past. This may be the local stellar population signature of the size evolution found for early-type galaxies from high-redshift observations.
AIP Conference Proceedings, 2009
We derive ages, metallicities and [a/Fe] ratios for dwarf early-type galaxies (dE/dSO) in the center and a region believed to be infalling into the Coma cluster We find that a set of metallic indices cannot be described by linear relations with velocity dispersion (a), while another group of indices exhibits linear index-c relations. dE/dSO galaxies in the core of the cluster are on average younger, and have lower metallicities and lower a-ratios (solar to sub-solar) than the more luminous elliptical galaxies. On the other hand, dEs/dSOs in the infall region of Coma form a less homogeneous population. We find an unusually high fraction of dE/dSOs with high [a/Fe] ratios, suggesting short time scales for the star formation histories for these galaxies. Furthermore, the dE/dSOs with high a-ratios have a range of ages and metallicities implying multiple formation scenarios where some galaxies have experienced their short star formation bursts at more recent epochs.