Quasar feedback: The missing link in structure formation

We consider the impact of quasar outflows on structure formation. Such outflows are potentially more important than galactic winds, which appear insufficient to produce the level of preheating inferred from X-ray observations of galaxy clusters. At late times, energetic material from the densest objects in the centers of galaxies makes its way into the intergalactic medium (IGM), impacting structures on many scales, much as supernovae impact structures on many scales within the interstellar medium. Using a simple analytical model for the distribution of quasars with redshift, coupled with a one-dimensional Sedov-Taylor model for outflows, we are able to make robust statements about these interactions. As large regions of the IGM are heated above a critical entropy of S_crit ≈ 100 keV cm², cooling becomes impossible within them, regardless of changes in density. On quasar scales, this has the effect of inhibiting further formation, resulting in their observed falloff in number densities below z ≈ 2. On galaxy scales, quasar feedback fixes the turnover scale in the galaxy luminosity function (L*) as the nonlinear scale at the redshift of strong feedback. The galaxy luminosity function then remains largely fixed after this epoch, consistent with recent observations and in contrast to the strong evolution predicted in more standard galaxy-formation models. Finally, strong quasar feedback explains why the intracluster medium is observed to have been preheated to entropy levels just above S_crit, the minimum excess that would not have been erased by cooling. The presence of such outflows is completely consistent with the observed properties of the Lyα forest at z ∼ 2 but is expected to have a substantial and detectable impact on Compton distortions observed in the microwave background and the multiphase properties of the "warm-hot" (z = 0) circumgalactic medium.