PRIMUS: An observationally motivated model to connect the evolution of the AGN and galaxy populations out to z~1
Publication information:
Aird J, Coil A, Moustakas J, Diamond-Stanic A, Blanton M, Cool R, Eisenstein D, Wong K, Zhu G. PRIMUS: An observationally motivated model to connect the evolution of the AGN and galaxy populations out to z~1. ArXiv e-prints. 2013;1301:1689.
Abstract
We present an observationally motivated model to connect the AGN andgalaxy populations at 0.21.0 and predict the AGN X-rayluminosity function (XLF). We start with measurements of the stellarmass function of galaxies (from the Prism Multi-object Survey) andpopulate galaxies with AGNs using models for the probability of a galaxyhosting an AGN as a function of specific accretion rate (the rate ofsupermassive black hole growth scaled relative to the host stellarmass). Our model is based on measurements indicating that the specificaccretion rate distribution is a universal function across a wide rangeof host stellar mass with slope gamma_1=0.65 and an overallnormalization that evolves strongly with redshift. We test severalsimple assumptions to extend this model to high specific accretion rates(beyond the measurements) and compare the predictions for the XLF withthe observed data. We find good agreement with a model that allows for abreak in the specific accretion rate distribution at a pointcorresponding to the Eddington limit, with a steep power-law tail tosuper-Eddington ratios with slope gamma_2=-2.1 +0.3 -0.5. We convertbetween specific accretion rate and Eddington ratio by assuming ascaling between black hole mass and host stellar mass with an intrinsicscatter of +/-0.38 dex. Our results show that samples of low luminosityAGNs are dominated by moderately massive galaxies (M* ~ 10^{10-11}M_sun) growing with a wide range of accretion rates -- a consequence ofthe shape of the galaxy stellar mass function rather than a preferencefor AGN activity at a particular stellar mass. The observed populationof the most luminous AGN may be severely skewed to the most extremesources with elevated black hole masses relative to their host galaxiesand in rare phases of very rapid accretion.