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OATS-DAUT SEMINAR
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Speaker: Giuseppe Gavazzi (Univ. Milano-Bicocca, Italy)
Title: A snapshot on galaxy evolution in the Great Wall:
Nature or Nurture? Nurture!
Date: Wednesday, March 24th, 2010
Time: 12:00
Venue: Villa Bazzoni
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Abstract: With the aim of quantifying the contribution of
the environment on the evolution of galaxies at z=0 we use the DR7
catalogue of the Sloan Digital Sky Survey (1) to reconstruct the 3-D
distribution of galaxies in the Coma supercluster, containing two rich
clusters (Coma and A1367), several groups and many filamentary
structures belonging to the "Great Wall". The color-luminosity
relation is derived for galaxies in two bins of morphological type and
in four thresholds of galaxy density, ranging from the loosest cosmic
web, the small groups, the large groups to the cluster's cores. A
well defined "red sequence" composed of early-type galaxies exists in
all environments at high luminosity, but it lacks of low luminosity
(dwarf) galaxies in the lowest density environment. Conversely low
luminosity isolated galaxies are predominantly of late-type. In other
words the low luminosity end of the distribution is dominated by red
dE galaxies in clusters and groups and by dwarf blue amorphous systems
in the lowest density regions. At z=0 we find evidence for strong
evolution induced by the environment (Nurture). Transformations take
place exclusively at low luminosity when star forming dwarf galaxies
inhabiting low density environments migrate into amorphous passive
dwarf ellipticals in their infall into denser regions. The mechanism
involves suppression of the star formation due to gas stripping,
without significant mass growth. Post-star-burst galaxies represent
the "carriers" of such transformation. They are the remnants of star
forming isolated galaxies that had their star formation violently
suppressed during their infall in clusters in the last 0.5-1.5 Gyrs,
and the progenitors of future dEs. They are found significantly
clustered around the largest dynamical units. Several examples of
galaxies currently undergoing transformations during their infall onto
the hot intracluster medium of A1367, a cluster much less-evolved than
Coma, are reviewed.
(1)The present "near-field cosmology" project makes use of the
photometry and the spectroscopy provided by the Sloan Digital Sky
Survey much in the way astronomers use telescopes in "service
observing" mode, but counting on an almost unlimited amount of
observing time.
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contact: Andrea Biviano (OATS)