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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)