The feedback of quasars on their galactic environment

Quasar outflows might either quench (negative) or enhance (positive feedback) star formation in galaxies located in the quasar environment. The possible outcome depend on 4 parameters: The quasar (σ) and satellite (σ*) halo velocity dispersion, their relative distance, d, and satellite disc radius, rd. We find that: (i) small satellites with σ∗<164 σ2/3200km s^−1 have their star formation quenched; (ii) in larger satellites, star formation, and hence UV/far-infrared (FIR) luminosity, is instead boosted by >80 per cent in a burst with typical duration of 5-10 Myr, if the following positive feedback criterion is met: d/rd < 15(Q/η)1/2σ200, where Q ≈ 1 is the satellite disc Toomre parameter; the disruption parameter (see equation 17) must be η > 1 to prevent complete satellite gas removal. We compare our predictions with ALMA data finding that observed satellites of z ≃ 6 QSOs on average form stars at a 3 × higher rate with respect to field galaxies at the same redshift. Further tests of the model are suggested.