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OATS-DAUT SEMINAR
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Speaker: David Wilman (MPE, Garching, D)

Title: Morphological Composition of z~0.4 Groups: The Site of S0 Formation?

Date: Wednesday, November 11th, 2009
Time: 12:00
Venue: Villa Bazzoni

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Abstract: The global budget of star formation in galaxies is regulated not only by gradual decline of star formation in individual galaxies, but also by mechanisms which completely suppress star formation and transform galaxy morphologies. The dramatic upturn in the fraction of lenticular (S0) galaxies in clusters since z~0.5 indicates that suppressing mechanisms at low z tend to preserve disks even in this extreme environment. To assess the role of more common environments, we present a morphological analysis of galaxies in optically-selected (spectroscopic friends-of-friends) group and field samples at z~0.4. Groups contain a much higher fraction of S0s at fixed luminosity than the lower density field, at least as high as typically found in clusters and X-ray selected groups at the same epoch. This, together with a slight preference for S0s to exist at the outskirts of groups, suggests that the bright X-ray emitting IGM cannot be important for the formation of the majority of S0s in the Universe. In contrast, the fraction of elliptical galaxies in groups at fixed luminosity is similar to the field, whilst the brightest ellipticals are strongly enhanced towards the group centres, consistent with a merger origin via dynamical friction.
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contact: Gabriella De Lucia (OATS)