Fabio Fontanot

INAF – OATS

torek, 5. 4. 2011, ob 14h v F5

The modeling of AGN feedback is of fundamental importance in order to understand the complex interplay between the various physical mechanisms shaping the observed properties of galactic populations and the evolution of their stellar masses and star formation rates. In particular, in the current theoretical paradigm of galaxy formation, AGN feedback plays a crucial role in regulating the levels of activity in galaxies, including the onset of cooling flows and star formation, as well as the triggering of galactic winds leading to the removal of the gas from the host galaxy. Only in recent years, however, the detailed study of the dependence of galaxy activity on stellar mass, parent halo mass and hierarchy (i.e. centrals or satellites) has been made possible thanks to the availability of large samples of galaxies and to the improved determination of their physical properties.

In my contribution, I will compare the fraction of galaxy belonging to different activity classes (i.e. star-forming, AGN and radio active) with the predictions of four semi-analytical models for galaxy formation and evolution, implementing different approaches for the growth of Supermassive Black Holes and the subsequent AGN feedback. I will employ empirical conversion laws to estimate the equivalents of the observed activity indicators from the predicted gas accretion rates ( line strength and radio power) and star formation rates ( emission line). I will demonstrate that the models are able to reproduce the overall distribution of the fraction of galaxies belonging to the different activity classes as a function of stellar mass and halo mass: star forming galaxies and strong radio sources are preferentially associated with low-mass and high-mass galaxies/halos respectively.

However, I will also highlight some relevant discrepancies between observations and model predictions. In SAMs predictions a relevant fraction of Dark Matter Halo with mass larger than solar masses and/or galaxy with mass larger than solar masses hosts a bright radio source and the radio brightness is expected to depend strongly on the mass of the parent halo mass, at variance with the available observational constraints. Finally I will also discuss the importance of the AGN fraction as a powerful discriminant between the different approaches to the problem of growth of Supermassive Black Holes.