Quasars: What Turns Them Off?

(Abridged) We explore the idea that the anti-hierarchical turn-off observedin the quasar population arises from self-regulating feedback, via an outflowmechanism. Using a detailed hydrodynamic simulation we calculate the luminosityfunction of quasars down to a redshift of z=1 in a large, cosmologicallyrepresentative volume. Outflows are included explicitly by tracking halomergers and driving shocks into the surrounding intergalactic medium. Ourresults are in excellent agreement with measurements of the spatialdistribution of quasars, and we detect an intriguing excess of galaxy-quasarpairs at very short separations. We also reproduce the anti-hierarchicalturnoff in the quasar luminosity function, however, the magnitude of theturn-off falls short of that observed as well as that predicted by analogoussemi-analytic models. The difference can be traced to the treatment of gasheating within galaxies. The simulated galaxy cluster L_X-T relationship isclose to that observed for z~1 clusters, but the simulated galaxy groups at z=1are significantly perturbed by quasar outflows, suggesting that measurements ofX-ray emission in high-redshift groups could well be a "smoking gun" for theAGN heating hypothesis.Comment: 16 pages, 11 figures, submitted to ApJ, comments welcome