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We present first results for spectroscopic observations of galaxies in 4 clusters at $z=0.7-0.8$ and one cluster at $z=0.5$ observed by the ESO Distant Cluster Survey (EDisCS). Our spectroscopic catalogues contain 236 cluster members of our 5 clusters, and the number of members per cluster ranges from 30 to 67. Our cluster velocity dispersions are between $\\sim$400 and over 1000 $\\rm{km s}^{-1}$. Galaxy redshift distributions are found to be non-Gaussian and we find evidence for significant substructure in two clusters, one at $z \\sim 0.79$ and another at $z \\sim 0.54$; both clusters have velocity dispersions exceeding 1000 $\\rm{km~s}^{-1}$. These systems have clearly not yet virialised at these epochs in qualitative agreement with CDM scenarios and their cluster velocity dispersions should not be used in the measurement of cluster mass. Our clusters have a wide range of different cluster velocity dispersions, richnesses and substructuring, and our spectroscopic data set is allowing a comprehensive insight into cluster galaxy evolution as a function of redshift and environment.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We study the evolution of spectral early-type galaxies in clusters, groups and the field up to redshift 0.9 using the EDisCS dataset. We measure Re, Ie, and sigma for 154 cluster and 68 field galaxies. We study the evolution of the zero point of the fundamental plane (FP) and confirm results in the literature, but now also for the low cluster velocity dispersion regime. The mass-to-light ratio varies as Delta log M/L_B=(-0.54+-0.01)z=(-1.61+-0.01)log(1+z) in clusters, independent of their velocity dispersion. The evolution is stronger (Delta log M/L_B=(-0.76+-0.01)z=(-2.27+-0.03)log(1+z)) for field galaxies. The FP residuals correlate with galaxy mass and become progressively negative at low masses. The effect is visible at z>=0.7 for cluster galaxies and at z>=0.5 for field galaxies. We investigate the size evolution of our galaxy sample. We find that the half-luminosity radius for a galaxy with a dynamical or stellar mass of 2x10^11 Msol varies as (1+z)^-1.0+-0.3 for both cluster and field galaxies. At the same time, stellar velocity dispersions grow with redshift, as (1+z)^0.59+-0.10 at constant dynamical mass, and as (1+z)^0.34+- 0.14 at constant stellar mass. The measured size evolution reduces to Re (1+z)^-0.5+- 0.2 and sigma (1+z)^0.41+-0.08, at fixed dynamical masses, and Re (1+z)^-0.68+-0.4 and sigma (1+z)^0.19+-0.10, at fixed stellar masses, when the progenitor bias (galaxies that locally are of spectroscopic early-type, but not very old, disappear from the EDisCS high-redshift sample; these galaxies tend to be large in size) is taken into account. Taken together, the variations in size and velocity dispersion imply that the luminosity evolution with redshift derived from the zero point of the FP is somewhat milder than that derived without taking these variations into account.

We analyse the rest–frame (U$-$V) colour–magnitude relation for 2 clusters at redshift 0.7 and 0.8, drawn from the ESO Distant Cluster Survey. By comparing them with the population of red galaxies in the Coma cluster, we show that the high redshift clusters exhibit a deficit of passive faint red galaxies. Our results show that the red–sequence population cannot be explained in terms of a monolithic and synchronous formation scenario. A large fraction of faint passive galaxies in clusters today has moved onto the red sequence relatively recently as a consequence of the fact that their star formation activity has come to an end at $z<0.8$.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a dynamical analysis of the merging galaxy cluster system Abell 2146 using spectroscopy obtained with the Gemini Multi-Object Spectrograph on the Gemini North telescope. As revealed by the Chandra X-ray Observatory, the system is undergoing a major merger and has a gas structure indicative of a recent first core passage. The system presents two large shock fronts, making it unique amongst these rare systems. The hot gas structure indicates that the merger axis must be close to the plane of the sky and that the two merging clusters are relatively close in mass, from the observation of two shock fronts. Using 63 spectroscopically determined cluster members, we apply various statistical tests to establish the presence of two distinct massive structures. With the caveat that the system has recently undergone a major merger, the virial mass estimate is M_vir = 8.5 +4.3 -4.7 x 10 ^14 M_sol for the whole system, consistent with the mass determination in a previous study using the Sunyaev-Zeldovich signal. The newly calculated redshift for the system is z = 0.2323. A two-body dynamical model gives an angle of 13-19 degrees between the merger axis and the plane of the sky, and a timescale after first core passage of 0.24-0.28 Gyr.

This paper reports the results obtained on the photometric redshifts measurement and accuracy, and cluster tomography in the ESO Distant Cluster Survey (EDisCS) fields. Photometric redshifts were computed using two independent codes (Hyperz and G. Rudnick's code). The accuracy of photometric redshifts was assessed by comparing our estimates with the spectroscopic redshifts of ~1400 galaxies in the 0.3

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