The massive black hole-velocity dispersion relation and the halo baryon fraction: a case for positive AGN feedback

Understand

Force balance considerations put a limit on the rate of AGN radiation momentum output, $L/c$, capable of driving galactic superwinds and reproducing the observed $\mbh -\sigma $ relation between black hole mass and spheroid velocity dispersion.

• We show that black holes cannot supply enough momentum in radiation to drive the gas out by pressure alone.
• Energy-driven winds give a $\mbh -\sigma $ scaling favoured by a recent analysis but also fall short energetically once cooling is incorporated.
• We propose that outflow-triggering of star formation by enhancing the intercloud medium turbulent pressure and squeezing clouds can supply the necessary boost, and suggest possible tests of this hypothesis.