The Abundance of Distant and Extremely Red Galaxies: The Role of AGN Feedback in Hierarchical Models

We investigate the effect of AGN feedback associated with the bright QSO phase on the color distribution of galaxies from z = 0 up to z = 4. To this aim, we insert a blast-wave model of AGN feedback in our semianalytic model of galaxy formation, which includes the growth of supermassive black holes and the AGN activity triggered by interactions of the host galaxies. The AGN feedback is directly related to the impulsive, luminous quasar phase. We test our model by checking the consistency of its results against (1) the QSO luminosity functions from z = 0 to 4, and (2) the observed local relation between the black hole mass m BH and the mass of the host galaxy. At low redshift the inclusion of AGN feedback enhances the number of red bright galaxies so that the color distribution of M r < -22 objects is entirely dominated by red ( u - r > 1.5) galaxies; at 0.5 < z < 2 it yields a rest-frame U - V color distribution, in agreement with existing observations. In the range z ≈ 1.5-2.5, we find that 31% of galaxies contribute to the extremely red object (ERO) population with m K < 20 (Vega system); at such a magnitude, the model yields an ERO surface density of 6.3 × 10 3 deg 2 , matching existing data. Extending our analysis to z = 4, the model matches the observed surface density 1.5 × 10 3 deg 2 of distant red galaxies (DRGs) at m K = 20; such a population is predicted to be dominated by galaxies with old stellar populations for z > 2.5.