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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)