Host galaxies of high-redshift quasars: SMBH growth and feedback

The properties of quasar-host galaxies might be determined by the growth and feedback of their supermassive black holes (SMBHs, 10(8-10) M-circle dot). We investigate such connection with a suite of cosmological simulations of massive (halo mass approximate to 10(12) M-circle dot) galaxies at z similar or equal to 6 that include a detailed subgrid multiphase gas and accretion model. BH seeds of initial mass 10(5) M-circle dot grow mostly by gas accretion, and become SMBH by z = 6 setting on the observed M-BH-M-star relation without the need for a boost factor. Although quasar feedback crucially controls the SMBH growth, its impact on the properties of the host galaxy at z = 6 is negligible. In our model, quasar activity can both quench (via gas heating) or enhance (by interstellar medium overpressurization) star formation. However, we find that the star formation history is insensitive to such modulation as it is largely dominated, at least at z > 6, by cold gas accretion from the environment that cannot be hindered by the quasar energy deposition. Although quasar-driven outflows can achieve velocities , only approximate to 4percent of the outflowing gas mass can actually escape from the host galaxy. These findings are only loosely constrained by available data, but can guide observational campaigns searching for signatures of quasar feedback in early galaxies.