The feedback of quasars on their galactic environment

Abstract

Quasar outflows might either quench (negative) or enhance (positive feedback) star formation in galaxies located in the quasar environment. The possible outcome depends on 4 parameters: the quasar ($\sigma$) and satellite ($\sigma_*$) halo velocity dispersion, their relative distance, $d$, and satellite disk radius, $r_d$. We find that: (i) small satellites with $\sigma _* < 164\ \sigma_{200}^{2/3}\, \rm km\ s^{-1}$ have their star formation quenched; (ii) in larger satellites, star formation, and hence UV/FIR luminosity, is instead boosted by $>80$\% in a burst with a typical duration of $5-10$ Myr, if the following positive feedback criterion is met: ${d}/{r_d} < 15 (Q/\eta)^{1/2} \sigma_{200}$, where $Q \approx 1$ is the satellite disk Toomre parameter; the disruption parameter (see eq. 17) must be $\eta>1$ to prevent complete satellite gas removal. We compare our predictions with ALMA data finding that observed satellites of $z\simeq 6$ QSOs on average form stars at a $3\times$ higher rate with respect to field galaxies at the same redshift. Further tests of the model are suggested.