A Unified, Merger‐driven Model of the Origin of Starbursts, Quasars, the Cosmic X‐Ray Background, Supermassive Black Holes, and Galaxy Spheroids

We present an evolutionary model for starbursts, quasars, and spheroidalgalaxies in which mergers between gas-rich galaxies drive nuclear inflows ofgas, producing intense starbursts and feeding the buried growth of supermassiveblack holes (BHs) until feedback expels gas and renders a briefly visibleoptical quasar. The quasar lifetime and obscuring column density depend on boththe instantaneous and peak luminosity of the quasar, and we determine thisdependence using a large set of simulations of galaxy mergers varying hostgalaxy properties, orbital geometry, and gas physics. We use these fits todeconvolve observed quasar luminosity functions (LFs) and obtain the evolutionof the formation rate of quasars with a certain peak luminosity, n(L_peak,z).Quasars spend extended periods of time at luminosities well below peak, and son(L_peak) has a maximum corresponding to the 'break' in the observed LF,falling off at both brighter and fainter luminosities. From n(L_peak) and oursimulation results, we obtain self-consistent fits to hard and soft X-ray andoptical quasar LFs and predict many observables, including: column densitydistributions of optical and X-ray samples, the LF of broad-line quasars inX-ray samples and the broad-line fraction as a function of luminosity, activeBH mass functions, the distribution of Eddington ratios at z~0-2, the z=0 massfunction of relic BHs and total mass density of BHs, and the cosmic X-raybackground. In every case, our predictions agree well with observed estimates,and unlike previous modeling attempts, we are able to reproduce them withoutinvoking any ad hoc assumptions about source properties or distributions. Weprovide a library of Monte Carlo realizations of our models for comparison withobservations. (Abridged)Comment: 50 pages, 25 figures. Accepted for publication in ApJS, March 2006. Revised and expanded with comments from referee repor