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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)