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OATS-UNI/TS SEMINAR
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Speaker: Laura Portinari (Dep. of Physics and Astronomy, Univ. of Turku, Finland)

Title: On the cosmological evolution of the black hole - host galaxy relation in quasars
Date: Wednesday, April 20th, 2011
Time: 15:00
Venue: Villa Bazzoni

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Abstract: We compare the expectations of Semi-Analytical Models (SAM) of galaxy evolution, to the largest available datasets on quasar host galaxies out to z <= 3. Observed quasars hosts are consistent with no evolution from the local MBH - Lhost relation, while SAM predict them to be sistematically brighter by about 1 magnitude. This overluminosity is partly a consequence of the fact that SAM associate quasars with recent mergers of galaxies, partly a problem of undermassive black holes, as models fail to reproduce the BH mass function in quasars at high z. The observations also suggest a significant increase of the mass ratio Gamma = MBH/M_*(host) from z=0 to z=3. Taken at face value, the observed strong evolution should favour SAM where quasar feedback plays a major role. However, we find that selection biases might still reconcile SAM that do not include quasar feedback with the observations. We suggest effective quasar feedback quenching star formation, combined with alternative mechanisms to form very massive black holes at high z, as a possible way to solve the overluminosity/undermassive black hole problem.
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Contact: Pierluigi Monaco (DAUT)