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OATS-DAUT SEMINAR
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Speaker: Fabio Fontanot (INAF/OATs)
Title: The Many Manifestations of Downsizing: Hierarchical Models
Confront Observations
Date: Wednesday, December 9th, 2009
Time: 12:00
Venue: Villa Bazzoni
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Abstract:
Several observations suggest that galaxy evolution follows a different
trend with respect to the bottom-up assembly of Dark Matter
structures. In this talk we discuss several observed trends for which
the word ``downsizing'' (DS) has been used, and in particular the
evolution with redshift of stellar mass (i.e. more massive galaxies
assemble earlier than low-mass counterparts), of the star formation
rate (i.e. the mass of typical star-forming galaxies declines with
decreasing redshift) and the ``archaeological'' DS (i.e. more massive
galaxies host the older stellar populations). We compare available
data-sets in the redshift range 0 < z < 4, with the predictions of
three different semi-analytical models of galaxy formation within the
LCDM framework. Despite the very different implementations, the three
models provide a coherent picture of the evolution of stellar mass and
star formation rate of galaxies. However, the models do not correctly
reproduce DS in stellar mass and archaeological DS, while DS in star
formation rate is roughly reproduced but with some important
discrepancies. At variance with many previous claims, we find that,
when a proper treatment of the observational error on mass and star
formation rate is performed, discrepancies on massive galaxies
(stellar mass > 1011 solar masses) weaken or disappear. At the same
time, lower mass galaxies (in the stellar mass range 109-11 solar
masses) are formed too early in the models (at z > 2-3 ) and are too
passive at late times. We demonstrate that this discrepancy is not
due to a poor description of the physics of satellite galaxies but is
connected to an excessively efficient formation of central galaxies in
high-redshift halos with circular velocities ~100 km/s.
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contact: Fabio Fontanot (OATS)