THE MASSIVE-BLACK-HOLE-VELOCITY-DISPERSION RELATION AND THE HALO BARYON FRACTION: A CASE FOR POSITIVE ACTIVE GALACTIC NUCLEUS FEEDBACK

Force balance considerations put a limit on the rate of active galactic nucleus radiation momentum output, L/c, capable of driving galactic superwinds and reproducing the observed MBH-σ 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-σ scaling favored 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. Our hypothesis simultaneously can account for the observed halo baryon fraction.