Feedback in Galaxy Formation

I review the outstanding problems in galaxy formation theory, and the role of feedback in resolving them. I address the efficiency of star formation, the galactic star formation rate, and the roles of supernovae and supermassive black holes.Comment: To appear in the proceedings of IAU Symposium 277, Burkina Faso, December 2010, Tracing the Ancestry of Galaxies (on the Land of our Ancestors), C. Carignan, F. Combes \& K. Freeman, ed

How the First Stars Regulated Local Star Formation I: Radiative Feedback

We present numerical simulations of how a 120 M$_\odot$ primordial star regulates star formation in nearby cosmological halos at $z \sim$ 20 by photoevaporation. Our models include nine-species primordial chemistry and self-consistent multifrequency conservative transfer of UV photons with all relevant radiative processes. Whether or not new stars form in halos clustered around a Population III star ultimately depends on their core densities and proximity to the star. Diffuse halos with central densities below 2 - 3 cm$^{-3}$ are completely ionized and evaporated anywhere in the cluster. Evolved halos with core densities above 2000 cm$^{-3}$ are impervious to both ionizing and Lyman-Werner flux at most distances from the star and collapse as quickly as they would in its absence. Star formation in halos of intermediate density can be either promoted or suppressed depending on how the I-front remnant shock compresses, deforms and enriches the core with H$_2$. We find that the 120 M$_\odot$ star photodissociates H$_2$ in most halos in the cluster but that catalysis by H- restores it a few hundred kyr after the death of the star, with little effect on star formation. Our models exhibit significant departures from previous one-dimensional spherically-symmetric simulations, which are prone to serious errors due to unphysical geometric focusing effects.Comment: 20 pages, 19 figures, accepted by ApJ, title and abstract change