Relating basic properties of bright early-type dwarf galaxies to their location in Abell 901/902 (original) (raw)

Young stellar populations in early-type dwarf galaxies

Astronomy & Astrophysics, 2019

Aims. To understand the stellar population content of early-type dwarf galaxies (dEs) and their environmental dependence, we compare the slopes and intrinsic scatter of color–magnitude relations (CMRs) for three nearby clusters, Fornax, Virgo, and Coma. Additionally, we present and compare internal color profiles of these galaxies to identify central blue regions with younger stars. Methods. We use the imaging of the HST/ACS Fornax cluster in the magnitude range of −18.7 ≤ Mg′ ≤ −16.0 to derive magnitudes, colors, and color profiles, which we compare with literature measurements from the HST/ACS Virgo and Coma Cluster Survey. We take advantage of HST accuracy to investigate and parameterize the (g′−z′) color profiles of these dEs. Results. Based on analysis of the color profiles, we report on a large number of dEs with young stellar populations at their center in all three clusters. While for Virgo and Coma the number of blue-cored dEs is found to be 85%±2% and 53%±3%, respectively,...

Properties of the Dwarf Galaxy Population in Galaxy Clusters

The Astrophysical Journal, 2008

We present the observational properties of the dwarf galaxy population (M r > M * r +1) corresponding to one of the largest samples of spectroscopically confirmed galaxy cluster members reported in the literature. We have observed that red dwarf galaxies (u−r > 2.22) share the same cluster environment as the brightest cluster members (M r < −21), but are not in dynamical equilibrium. We computed the dwarf-to-giant ratio (DGR) using a spectroscopically selected sample. The DGR was found to vary with clustercentric distance, essentially due to the blue dwarf population (u − r < 2.22). The u − r color of red dwarf galaxies was independent of their environment and similar to the color of red isolated dwarfs. Blue dwarf galaxies located outside r 200 show similar u − r colors to those of the field population, while strong reddening was observed toward the cluster center. We also present evidence that the fraction of red to blue dwarf galaxies in clusters is larger in the innermost cluster regions. We conclude that the present red dwarf population observed in the central regions of nearby galaxy clusters could be related to the blue dwarf population observed in clusters at high redshift.

Structure and stellar content of dwarf galaxies

Astronomy and Astrophysics Supplement Series, 2000

CCD photometry in the Cousins B, V and R bands of 19 northern field dwarf galaxies is presented. For each galaxy, and for each colour, we determined total magnitude, effective radius and effective surface brightness, and, by fitting an exponential to the surface brightness profile, central surface brightness and exponential scale length. Surface brightness and colour profiles are shown. One of the observed galaxies (UGC 2689) is probably a background S0 galaxy and belongs to the cluster Abell 426. All others, with one possible exception (Kar 49), are typical late-type field dwarf galaxies (mostly magellanic irregulars) lying in the distance range 5-10 Mpc. The sample has a median absolute magnitude MB = −14.9 and a median colour (B − V) = 0.52. The present latetype dwarfs have higher surface brightness in the mean than cluster late-type dwarfs, confirming a trend found in our previous work. However, there is no evidence for a photometric difference between field and group late-type dwarfs. This paper is part of a long-term programme to study the environmental differences in the photometric structure of dwarf galaxies.

Dwarf elliptical galaxies: structure, star formation and colour-magnitude diagrams

Monthly Notices of the Royal Astronomical Society, 2001

The aim of this paper is to cast light on the formation and evolution of elliptical galaxies by means of N-body hydrodynamical simulations that include star formation, feedback and chemical evolution. Particular attention is paid to the case of dwarf spheroidals of the Local Group which, thanks to their proximity and modern ground-based and space instrumentation, can be resolved into single stars so that independent determinations of their age and star formation history can be derived. Indeed, the analysis of the colour-magnitude diagram of their stellar content allows us to infer the past history of star formation and chemical enrichment, thus setting important constraints on galactic models. Dwarf galaxies are known to exhibit complicated histories of star formation ranging from a single very old episode to a series of bursts over most of the Hubble time. By understanding the physical process driving star formation in these objects, we might be able to infer the mechanism governing star formation in more massive elliptical galaxies. Given these premises, we start from virialized haloes of dark matter, and follow the infall of gas into the potential wells and the formation of stars. We find that in objects of the same total mass, different star formation histories are possible, if the collapse phase started at different initial densities. We predict the final structure of dwarf spheroidal galaxies, their kinematics, their large-scale distribution of gas and stars, and their detailed histories of the star formation and metal enrichment. Using a population synthesis technique, star formation and metal enrichment rates are then adopted to generate the present colour-magnitude diagrams of the stellar populations hosted by dwarf spheroidal galaxies. The simulations are made assuming the redshift of galaxy formation z for ¼ 5 and varying the cosmological parameters H 0 and q 0. The resulting colour-magnitude diagrams are then compared with the observational ones for some dwarf spheroidals of the Local Group.

Surface Brightness Profiles of Dwarf Galaxies. II. Color Trends and Mass Profiles

The Astronomical Journal, 2016

In this second paper of a series, we explore the B − V , U − B, and FUV−NUV radial color trends from a multi-wavelength sample of 141 dwarf disk galaxies. Like spirals, dwarf galaxies have three types of radial surface brightness profiles: (I) single exponential throughout the observed extent (the minority), (II) down-bending (the majority), and (III) up-bending. We find that colors of (1) Type I dwarfs generally become redder with increasing radius unlike spirals that have a blueing trend that flattens beyond ∼1.5 disk scale lengths, (2) Type II dwarfs come in six different "flavors," one of which mimics the "U" shape of spirals, and (3) Type III dwarfs have a stretched "S" shape where central colors are flattish, become steeply redder to the surface brightness break, then remain roughly constant beyond, similar to spiral Type III color profiles, but without the central outward bluing. Faint (−9 > M B > −14) Type II dwarfs tend to have continuously red or "U" shaped colors and steeper color slopes than bright (−14 > M B > −19) Type II dwarfs, which additionally have colors that become bluer or remain constant with increasing radius. Sm dwarfs and BCDs tend to have at least some blue and red radial color trend, respectively. Additionally, we determine stellar surface mass density (Σ) profiles and use them to show that the break in Σ generally remains in Type II dwarfs (unlike Type II spirals) but generally disappears in Type III dwarfs (unlike Type III spirals). Moreover, the break in Σ is strong, intermediate, and weak in faint dwarfs, bright dwarfs, and spirals, respectively, indicating that Σ may straighten with increasing galaxy mass. Lastly, the average stellar surface mass density at the surface brightness break is roughly 1−2 M ⊙ pc −2 for Type II dwarfs but higher at 5.9 M ⊙ pc −2 or 27 M ⊙ pc −2 for Type III BCDs and dIms, respectively.

Morphologies and stellar populations of galaxies in the core of Abell 2218

Monthly Notices of the Royal Astronomical Society, 2007

We present a study of the stellar populations and morphologies of galaxies in the core of the galaxy cluster Abell 2218. Integral field spectroscopy (IFS) observations were performed using PMAS in the PPAK mode covering a field-of-view of ∼74"×64" centred on the core of the cluster, in order to obtain spectroscopy of an unbiased flux limited sample of cluster galaxies. Forty-three objects were detected in the IFS data, 31 of them with enough signal-to-noise to derive the redshift, all of them brighter than I <21.5 mag. Twenty-eight are at the redshift of the cluster (17 with previously unknown redshift). Individual spectra of the cluster members were extracted and compared with single stellar population models to derive the luminosity-weighted ages and metallicities. In addition, deep HST/ACS F475W, F555W, F625W and F850LP-band images centred on the cluster core were obtained from the HST archive (z lim ∼28 mag). A detailed morphological analysis of all the galaxies within the field-of-view of these images down to z lim <22.5 mag was performed classifying them as late-type, intermediate and early-type, on the basis of their Sérsic indices. The literature was scanned to look for spectroscopically confirmed cluster members located within the field-of-view of the ACS image. The final sample of 59 galaxies comprises our reported sample of 28 galaxies in the core, and 31 additional galaxies in the outer regions. In addition, multiband broad-band photometry was extracted from the literature for all objects.

Galaxy populations in the Antlia cluster - I. Photometric properties of early-type galaxies

Monthly Notices of The Royal Astronomical Society, 2008

We present the first colour-magnitude relation (CMR) of early-type galaxies in the central region of the Antlia cluster, obtained from CCD wide-field photometry in the Washington photometric system. Integrated (C - T1) colours, T1 magnitudes, and effective radii have been measured for 93 galaxies (i.e. the largest galaxies sample in the Washington system till now) from the FS90 Antlia Group catalogue. Membership of 37 objects can be confirmed through new radial velocities and data collected from the literature. The resulting colour-magnitude diagram shows that early-type FS90 galaxies that are spectroscopically confirmed Antlia members or that were considered as definite members by FS90, follow a well-defined CMR that spans 9 mag in brightness with no apparent change of slope. This relation is very tight for the whole magnitude range but S0 galaxies show a larger dispersion, apparently due to a separation of ellipticals and S0s. Antlia displays a slope of -13.6 in a T1 versus (C - T1) diagram, in agreement with results for clusters like Fornax, Virgo, Coma and Perseus, which are dynamically different to Antlia. This fact might indicate that the build-up of the CMR in cluster of galaxies is more related to galaxies internal processes than to the influence of the environment. Interpreting the CMR as a luminosity-metallicity relation of old stellar systems, the metallicities of the Antlia galaxies define a global relation down to MV ~ -13. We also find, for early-type dwarfs, no clear relation between luminosity and effective radius, indicating a nearly constant mean effective radius of ~1 kpc. This value is also found in several samples of dwarf galaxies in Virgo and Coma. This paper is based on data obtained with the 4-m telescope at CTIO, Chile, with the 6.5-m Magellan telescopes at Las Campanas Observatory, Chile, and at CASLEO, operated under agreement between CONICET and the Universities of La Plata, Córdoba and San Juan, Argentina. E-mail: asmith@fcaglp.unlp.edu.ar (AVSC); lbassino@fcaglp.unlp.edu.ar (LPB); tom@mobydick.cfm.udec.cl (TR); scellone@fcaglp.unlp.edu.ar (SAC); linfante@astro.puc.cl (LI) ‡ In memoriam.

Galaxy populations in the Antlia cluster - III. Properties of faint early-type galaxies★

Monthly Notices of the Royal Astronomical Society, 2011

We present a new analysis of the early-type galaxy population in the central region of the Antlia cluster, focusing on the faint systems such as dwarf ellipticals (dEs) and dwarf spheroidals (dSphs). The colour-magnitude relation (CMR) and the relation between luminosity and mean effective surface brightness for galaxies in the central region of Antlia have been previously studied in Paper I of the present series. Now we confirm 22 early-type galaxies as Antlia members, using Gemini-GMOS and Magellan-MIKE spectra. Among them, 15 are dEs from the FS90 Antlia Group catalogue, two belong to the rare type of compact ellipticals (cEs) and five are new faint dwarfs that had never been catalogued before. In addition, we present 16 newly identified low-surface-brightness galaxy candidates, almost half of them displaying morphologies consistent with being Antlia's counterparts of Local Group dSphs, which extend the faint luminosity limit of our study down to M B = −10.1(B T = 22.6) mag. With these new data, we built an improved CMR in the Washington photometric system, i.e. integrated T 1 magnitudes versus (C − T 1) colours, which extends ∼4 mag faintwards the limit of spectroscopically confirmed Antlia members. When only confirmed early-type members are considered, this relation extends over 10 mag in luminosity with no apparent change in slope or increase in colour dispersion towards its faint end. The intrinsic colour scatter of the relation is compared with those reported for other clusters of galaxies; we argue that it is likely that the large scatter of the CMR, usually reported at faint magnitudes, is mostly due to photometric errors along with an improper membership/morphological classification. The distinct behaviour of the luminosity versus mean effective surface brightness relation at the bright and faint ends is analysed, while it is confirmed that dE galaxies on the same relation present a very similar effective radius, regardless of their colour. The projected spatial distribution of the member sample confirms the existence of two groups in Antlia, each one dominated by a giant elliptical galaxy and with one cE located close to each giant. Size and position, with respect to massive galaxies, of the dSph candidates are estimated and compared to Local Group counterparts.

The red and blue galaxy populations in the GOODS field: evidence for an excess of red dwarfs

Astronomy and Astrophysics, 2008

Aims. We study the evolution of the galaxy population up to z ∼ 3 as a function of its colour properties. In particular, luminosity functions and luminosity densities have been derived as a function of redshift for the blue/late and red/early populations. Methods. We use data from the GOODS-MUSIC catalogue which have typical magnitude limits z 850 ≤ 26 and K s ≤ 23.5 for most of the sample. About 8% of the galaxies have spectroscopic redshifts; the remaining have well calibrated photometric redshifts derived from the extremely wide multi-wavelength coverage in 14 bands (from the U band to the Spitzer 8µm band). We have derived a catalogue of galaxies complete in rest-frame B-band, which has been divided in two subsamples according to their rest-frame U-V colour (or derived specific star formation rate, SSFR) properties. Results. We confirm a bimodality in the U-V colour and SSFR of the galaxy sample up to z ∼ 3. This bimodality is used to compute the LFs of the blue/late and red/early subsamples. The LFs of the blue/late and total samples are well represented by steep Schechter functions evolving in luminosity with increasing redshifts. The volume density of the LFs of the red/early populations decreases with increasing redshift. The shape of the red/early LFs shows an excess of faint red dwarfs with respect to the extrapolation of a flat Schechter function and can be represented by the sum of two Schechter functions. Our model for galaxy formation in the hierarchical clustering scenario, which also includes external feedback due to a diffuse UV background, shows a general broad agreement with the LFs of both populations, the larger discrepancies being present at the faint end for the red population. Hints on the nature of the red dwarf population are given on the basis of their stellar mass and spatial distributions.

Photometric and Morphological Properties of Nearby Cluster Galaxies

The Astrophysical Journal Supplement Series, 2004

Photometric observations are presented for 8747 galaxies in the fields of 28 clusters with redshifts in the range 0:05 < z < 0:11 and spanning a wide range in Abell richness class. The primary motivation for this study is to provide a nearby sample of clusters whose galaxy populations can be used to provide an anchor point for evolutionary studies of cluster galaxy populations. The present analysis focuses on the sequence of luminous red galaxies that form a tight correlation in the colormagnitude plane. An ensemble cluster constructed from the full sample shows the red sequence clearly and the observed dispersion-not corrected for observational errors-is (V À I) ¼ 0:071 AE 0:006 down to M I(AB) ¼ À19:5. Selecting only early-type galaxies on the basis of their fractional bulge luminosity (B=T) reduces the observed dispersion to (V À I) ¼ 0:050 AE 0:006 mag, a significantly smaller dispersion than the full sample at more than the 95% confidence level. The slope of the color-magnitude relation in (V À I)=I is À0:023 AE 0:006. This set of clusters shows a red sequence that has the same mean color in all clusters (V À I) AB ¼ 0:91 AE 0:03 (measured at M I(AB) ¼ À23) and has the same intrinsic dispersion, (V À I) ¼ 0:04 AE 0:01, in all clusters within the observational errors. Thus, these clusters form a remarkably homogeneous family as represented by their luminous red galaxy populations.