The structure and galaxy populations of distant clusters of galaxies

Outstanding questions in modern cosmology are how and when elliptical galaxies - the most massive galaxies known - were formed. Another important issue is the evolution of the star formation activity in the galaxy populations of clusters. Studies in different density environments, in particular high redshift clusters, are necessary to improve our knowledge on these subjects. Under this scope, an unpresedented panchromatic study of 7 clusters of galaxies in the redshift range 0.8 < z < 1.3 is being carried out with the HST/ACS as part of the ACS cluster progam, supported by ESO NTT and VLT, Keck, Chandra and XMM observations.  My Ph.D. research was mainly concentrated on the analysis of ESO VLT/FORS spectroscopic data of two of these clusters:  RXJ0152 (z=0.84) and RDCS1252 (z=1.24). The spectroscopic data was used to characterize the distribution and dynamical state of the galaxy population in each cluster as well as to derive velocity dispersions and cluster masses. This information was compared to X-ray observations of the ICM gas and DM distribution from weak lensing studies to obtain a comprehensive view of the overall structure of these clusters. The photometric properties of early-type galaxies in these clusters indicate that the bulk of the stars in massive elliptical galaxies is old, with a mean formation epoch  at  z~3,  and that these galaxies evolved passively since their formation.  The spectroscopic data also reveal a spatial segregation between passive galaxies and star-forming galaxies: the latter are observed to avoid the high density regions of clusters which are dominated by passive (non star-forming) galaxies. This observation may provided important clues to understand galaxy evolution in cluster environments. See: Demarco et al. 2005, A&A, 432, 381; Homeier et al. 2005, ApJ, 621, 651; Jee et al. 2005, ApJ, 618, 46; Lombardi et al. 2005, ApJ, 623, 42; Postman et al. 2005, ApJ, 623, 721; Rosati et al. 2004, AJ, 127, 230; Lidman et al. 2004, A&A, 416, 829; Toft et al. 2003, A&A, 422, 29; Blakeslee et al. 2003, ApJ, 596L, 143.

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