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OATS-DAUT SEMINAR
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Speaker: Joana Santos (INAF/OATS, I)

Title: The galaxy population of an X-ray luminous Galaxy Cluster at redshift z~1

Date: Wednesday, March 25th, 2009
Time: 12:00
Venue: Villa Bazzoni

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Abstract:
Distant (z~1) galaxy clusters are unique astrophysical laboratories particularly suited to study the evolution of early-type galaxies (ETGs), and thus constrain their formation epoch. The colour-magnitude relation (CMR) is a fundamental scaling relation characterized by an ubiquitous Red Sequence formed of massive red elliptical galaxies undergoing passive evolution. The analysis of its main parameters: zero point, scatter and slope, provide a means to quantify the evolution of the galaxy properties with redshift. However, the measurement of accurate colours, as well as a reliable morphological analysis of high-z galaxies, require data with high resolution and sensitivity, which is optimally achieved by the Advanced Camera for Surveys (ACS) at the Hubble Space Telescope. We present a multi-wavelength analysis of the galaxy properties in XMMU J1229+0151, an X-ray selected, rich and distant cluster (z=0.975 corresponding to a lookback time of 7.6 Gyr). The high-quality ACS i775- and z850-band imaging allowed us to derive accurate galaxy photometry and characterize the galaxies morphology via visual inspection and by fitting Sersic surface brightness profiles. With the additional ground-based NIR J- and Ks-bands, combined with the optical FORS2 spectra, we performed an SED analysis with which we derived galaxy stellar masses and ages. The star formation histories of the cluster's ETGs are derived by fitting the coadded spectrophotometric data using Bruzual & Charlot (2003) templates. The results show a red-sequence populated by galaxies with stellar masses in the range 5E10 - 2E11 Msun and old (3-4 Gyr) underlying stellar populations formed at zf~4. The CMR at this high redshift is found to be already very tight, with a spread of only 0.04. This is in agreement with current observational evidence that ETGs in clusters assembled early on and in short timescales, and their star formation processes have already completed the essential part of their chemical enrichment, as elucidated by the high metal abundance (Z ~ 0.3 solar) of the intracluster medium, measured with XMM spectra.
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contact: Joana Santos (OATS)