Scientific Seminars

Feedback effects of black holes during reionization

E. Ripamonti
Universita' dell'Insubria

2008-03-10    11.00    Merate -

The observation of bright quasars at z~6 suggests that massive and luminous BHs were present at even earlier epochs. Starting from semi-analytical models of the evolution of the cosmological density of BHs, I look at the feedback effects of their emission during the reionization epoch (30>~ z >~ 5). I find that the "neutral" IGM (i.e. the regions which are reionized late, as they are removed from luminous sources) is easily heated to ~ 1000-10000 K by the soft X-rays produced by BHs; this should leave an observable signature upon the 21 cm emission. Furthermore, the heating of the IGM increases the "critical mass" an halo needs in order for its gas to be able to cool, collapse and form stars: at z<~10 such mass goes from 105-106 Msun to 107-108 Msun, and the formation of low mass halos is largely suppressed. This last effect is even stronger when the surroundings of a BH are considered, both because the critical mass is raised to higher levels, and because even halos above the critical mass can lose a large fraction of their gas.