Evolutionary features in distant clusters of galaxies

The Astrophysical Journal, 1999

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.

Astronomy and Astrophysics, 1996

At B magnitudes > ∼ 24 there is a well-known excess of galaxies (compared to standard models) which is probably due to an (evolving) population of sub-L * galaxies at moderate redshifts ( < ∼ 0.4). One particular hypothesis which is hard to test directly via number counts or even redshift surveys is the possibility that the faint blue galaxies are in fact sub-galactic objects destined to merge by the present day to form current giant galaxies. If this were the case we might expect to find the faint blue galaxies in the vicinity of L * galaxies (at redshifts 0.2 to 0.4) with which they can merge (the blue galaxies are already known to be weakly clustered among themselves, limiting the possibility for multiple mergers of small fragments).

Monthly Notices of The Royal Astronomical Society, 1998

We present the radial velocities and blue, optical magnitudes for all of the galaxies within the Durham/UKST Galaxy Redshift Survey. This catalogue consists of ϳ2500 galaxy redshifts to a limiting apparent magnitude of b J Ӎ 17 mag, covering a ϳ1500-deg 2 area around the South Galactic Pole. The galaxies in this survey were selected from the Edinburgh/Durham Southern Galaxy Catalogue and were sampled, in order of apparent magnitude, at a rate of one galaxy in every three. The spectroscopy was performed at the 1.2-m UK Schmidt Telescope in Australia using the FLAIR multi-object spectrograph. We show that our radial velocity measurements made with this instrument have an empirical accuracy of Ϯ150 km s ¹1 . The observational techniques and data reduction procedures used in the construction of this survey are also discussed. This survey demonstrates that the UKST can be used to make a three-dimensional map of the large-scale galaxy distribution, via a redshift survey to b J Ӎ 17 mag, over a wide area of the sky.

Astronomy and Astrophysics Supplement Series, 1998

The detailed surface photometry of a sample of early-type galaxies in the Hubble Deep Field is presented as part of a long-term project aimed to settle strong observational constraints to the theories modelling the evolution of elliptical galaxies from the early stages. The sample has been extracted, in the V 606 band, from the database provided by the ESO-ST ECF -HDF Group . The selection criteria involve the total magnitude, the number of pixels detected above the background level and an automatic star/galaxy classifier. Moreover, form visual inspection of the frames, we excluded the galaxies showing unambiguous late-type morphology. The analysis of the luminosity and geometrical profiles, carried out on the 162 candidates obeying our selection criteria, resulted in a list of 99 "bona fide" earlytype galaxies, for which accurate total magnitudes and effective radii were computed on the basis of the equivalent luminosity profiles. The comparison with the magnitudes given by Williams et al. (1996) indicates that the automated photometry tends to underestimate the total luminosity of the ellipticals. The luminosity profiles of most of galaxies in our sample follow fairly well the de Vaucouleurs law ("Normal" profiles). However, a relevant fraction of galaxies, even following the r 1/4 law in the main body light distribution, exhibit in the inner region a flattening of the luminosity profile not attributable to the P SF ("Flat" profiles) or, in some cases, a complex (multi-nucleus) structure ("Merger" profiles). A statistically significant correlation is found between the shapes of the luminosity profiles and the ellipticity distribution. In particular, the average ellipticity of galaxies belonging to the "Flat" and "Merger" classes is significantly higher than that of the "Normal" galaxies. Finally, even taken into account the relevant un-Send offprint requests to: G. Fasano Complete Table is available electronically at the CDS at ftp 130.79.128.5 and Fig. is can be accessed on the online version of the journal (). certainty of the outer position angle profiles, the amount of isophotal twisting of HDF ellipticals turns out to be significantly larger with respect to that of the local samples.

The Astronomical Journal, 1998

We present a description of the observations and data reduction procedures for an extensive spectroscopic and multi-band photometric study of nine high redshift, optically-selected cluster candidates. The primary goal of the survey is to establish new constraints on cluster and galaxy evolution, with specific emphasis on the evolution of galaxy morphology and on the star-formation history of the galaxies within and around distant clusters. We have measured 892 new redshifts for galaxies with R ≤ 23.3. The data will also serve as deep probes of the foreground and background large-scale structures. The observations include broad band optical imaging and spectroscopy with the Low Resolution Imaging Spectrograph at the 10 meter W. M. Keck Observatory telescope; K-band imaging with IRIM at the 4 meter Kitt Peak National Observatory telescope; and deep, high angular resolution imaging with the WFPC2 onboard the Hubble Space Telescope. We also describe the procedures used to obtain morphological information. We have established that six of the nine cluster candidates are indeed real space density enhancements and are representative of those typically associated with clusters of galaxies. The remaining three candidates appear to be projections of several smaller groups at widely separated distances. This success rate is consistent with estimates of the false positive rate in 2D optical high-z cluster searches.

Astronomical Journal, 2002

This paper presents data on the ENEARc subsample of the larger ENEAR survey of nearby early-type galaxies. The ENEARc galaxies belong to clusters and were specifically chosen to be used for the construction of a D n -template. The ENEARc sample includes new measurements of spectroscopic and photometric parameters (redshift, velocity dispersion, line index Mg 2 , and the angular diameter d n ), as well as data from the literature. New spectroscopic data are given for 229 cluster early-type galaxies, and new photometry is presented for 348 objects. Repeat and overlap observations with external data sets are used to construct a final merged catalog consisting of 640 early-type galaxies in 28 clusters. Objective criteria, based on catalogs of groups of galaxies derived from complete redshift surveys of the nearby universe, are used to assign galaxies to clusters. In a companion paper, these data are used to construct the template D n -distance relation for early-type galaxies, which has been used to estimate galaxy distances and derive peculiar velocities for the ENEAR all-sky sample.

arXiv (Cornell University), 1998

A "friends-of-friends" percolation algorithm has been used to extract a catalogue of δρ/ρ = 80 density enhancements (groups) from the six slices of the Las Campanas Redshift Survey (LCRS). The full catalogue contains 1495 groups and includes 35% of the LCRS galaxy sample. A statistical sample of 394 groups has been derived by culling groups from the full sample which either are too close to a slice edge, have a crossing time greater than a Hubble time, have a corrected velocity dispersion of zero or less, or contain a 55 arcsec "orphan" (a galaxy with a "faked" redshift excluded from the original LCRS redshift catalogue due to its proximity-i.e., within 55 arcsec-of another galaxy). Median properties derived from the statistical sample include: line-of-sight velocity dispersion σ los = 164 km s −1 , crossing time t cr = 0.10 H −1 0 , harmonic radius R h = 0.58 h −1 Mpc, pairwise separation R p = 0.64 h −1 Mpc, virial mass M vir = 1.90 × 10 13 h −1 M sun , total group R-band luminosity L tot = 1.40 × 10 11 h −2 L sun , and R-band mass-to-light ratio M/L = 153 h M sun /L sun .

Astronomical Journal, 2002

In this paper R-band photometric and velocity dispersion measurements for a sample of 452 elliptical and S0 galaxies in 28 clusters are used to construct a template D_n-sigma relation. This template relation is constructed by combining the data from the 28 clusters, under the assumption that galaxies in different clusters have similar properties. The photometric and spectroscopic data used consist of new as well as published measurements, converted to a common system, as presented in a accompanying paper. The resulting direct relation, corrected for incompleteness bias, is log{D_n} =1.203 log{sigma} + 1.406; the zero-point has been defined by requiring distant clusters to be at rest relative to the CMB. This zero-point is consistent with the value obtained by using the distance to Virgo as determined by the Cepheid period-luminosity relation. This new D_n-sigma relation leads to a peculiar velocity of -72 (\pm 189) km/s for the Coma cluster. The scatter in the distance relation corresponds to a distance error of about 20%, comparable to the values obtained for the Fundamental Plane relation. Correlations between the scatter and residuals of the D_n-sigma relation with other parameters that characterize the cluster and/or the galaxy stellar population are also analyzed. The direct and inverse relations presented here have been used in recent studies of the peculiar velocity field mapped by the ENEAR all-sky sample.

New Light on Galaxy Evolution, 1996

Astrophys J, 1995

Hubble Space Telescope 1 B and I images are presented of 32 galaxies with secure redshifts in the range 0:5 < z < 1:2 from the Canada-France Redshift Survey, a complete sample of galaxies with 17:5 I AB 22:5. These galaxies exhibit the same range of morphological types as seen locally, i.e., ellipticals, spirals and irregulars. The galaxies look far less regular in the B images (rest-frame ultraviolet) than at longer wavelengths, underlining the fact that optical images of galaxies at still higher redshift should be interpreted with caution.

The Astrophysical Journal Supplement Series, 2000

Utilizing the F814W and F300W filters, Hubble Space Telescope Wide Field Planetary Camera-2 (WFPC2) images were taken of four low surface brightness galaxies in the direction of the Virgo cluster -V7L3, V2L8, V1L4, and Malin 1. The high resolution of the WFPC2 combined with the extremely diffuse nature of the four galaxies makes them essentially transparent, allowing for the serendipitous discovery of 139 background galaxies visible through both the disks and nuclei of the foreground galaxies. Surface photometry was done on the newly discovered galaxies through the F814W (I-band) filter. The detected galaxies have both r 1/4 and exponential type profiles with radii (to the µ F 814W = 25.0 mag arcsec −2 limit) less than 5.0". Their total magnitudes range from 18.9 through the survey cut-off at 25.0 in the F814W filter. The median central surface brightness of those galaxies with exponential profiles is approximately one magnitude brighter than the background F814W "sky". Thus, with this dataset we recover Freeman's law and hence know that we do not have a representative sample of distant galaxies (and neither does anyone else). When possible, the B, V, and I colors of these galaxies were determined using ground-based images, which show the galaxies to be fairly red. Coupled with their small angular size, we estimate the redshifts to be 0.5 ≤ z ≤ 1.5.

Monthly Notices of the Royal Astronomical Society, 2014

We have used GALEX and SDSS observations to extract 7 band photometric magnitudes for over 80,000 objects in the vicinity of the North Galactic Pole. Although these had been identified as stars by the SDSS pipeline, we found through fitting with model SEDs that most were, in fact, of extragalactic origin. Only about 9% of these objects turned out to be main sequence stars and about 11% were white dwarfs and red giants collectively, while galaxies and quasars contributed to the remaining 80% of the data. We have classified these objects into different spectral types (for the stars) and into different galactic types (for the galaxies).

The Astronomical Journal

To understand the range of morphologies observed in the galaxy population at high redshift, it is instructive to evaluate the appearance of local peculiar galaxies when placed at cosmological distances. To this end, we use rest frame ultraviolet (UV), B, and V band images of five nearby (z < 0.02) interacting and/or starbursting galaxies to simulate deep HST observations of peculiar galaxies at medium to high redshifts. In particular, we simulate Hubble Deep Field (HDF) observations in the F606W and F814W filters of starburst galaxies in the redshift range z∼0.5-2.5 by explicitly account for the combined effects of band-shifting and surface brightness dimming. We find that extended morphological features remain readily visible in the long exposures typical of the HDF out to redshifts of ∼1. For systems above z ≈1.5, the simulated morphologies look remarkably similar to those of the faint objects found in the HDF and other deep HST fields. Peculiar starburst galaxies therefore appear to be the best local analogs to the highest redshift galaxies in terms of morphology, star formation rates, and spectral energy distributions. Nevertheless, photometric measurements of the z > 1.5 images fail to recover the true global properties of the underlying systems. This is because the high-z observations are sensitive to the rest-frame UV emission, which is dominated by the most active star forming regions. The extended distribution of starlight from more evolved populations would not be detected. Therefore, while the observed morphologies provide information on the distribution of star formation within the systems, they may reveal very little about their true dynamical states. We conclude that imaging observations in the restframe UV alone cannot reveal whether high-z systems (z ∼ >1.5) are proto-galaxies, proto-bulges, or starbursts within a pre-existing population. Definitive statements regarding the global properties and dynamical states of these objects require deep imaging observations at longer wavelengths.

2000

In this paper we identify objectively and analyze groups of galaxies in the recently completed ESP survey (23 h 23 m ≤ α 1950 ≤ 01 h 20 m and 22 h 30 m ≤ α 1950 ≤ 22 h 52 m ; −40 o 45 ≤ δ 1950 ≤ −39 o 45 )