The feedback of quasars on their galactic environment

Andrea Ferrara, Tommaso Zana, Simona Gallerani, Laura Sommovigo

Published 2023-01-25Version 1

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.