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

Abstract

We investigate the effect of AGN feedback associated to the bright QSO phase onto 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 semi-analytic 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 i) the QSO luminosity functions from z=0 to z=4; ii) 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 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 EROs population with m_K<20 (Vega system); at such a magnitude, the model yields an EROs surface density of 6.3 10^3 /deg^2 matching existing data; about 80 % of the above density is contributed by passive galaxies with old stellar populations. Extending our analysis to z=4, the model matches the observed surface density 1.5 10^3 /deg^2 of DRGs at m_K=20; such a population is predicted to be dominated by galaxies with old stellar populations for z>2.5.