Massive and Red Objects Predicted by a Semianalytical Model of Galaxy Formation

We study whether hierarchical galaxy formation in a concordance $\Lambda$CDMuniverse can produce enough massive and red galaxies compared to theobservations. We implement a semi-analytical model in which the central blackholes gain their mass during major mergers of galaxies and the energy feedbackfrom active galaxy nuclei (AGN) suppresses the gas cooling in their host halos.The energy feedback from AGN acts effectively only in massive galaxies whensupermassive black holes have been formed in the central bulges. Compared withprevious models without black hole formation, our model predicts more massiveand luminous galaxies at high redshift, agreeing with the observations of K20up to $z\sim 3$. Also the predicted stellar mass density from massive galaxiesagrees with the observations of GDDS. Because of the energy feedback from AGN,the formation of new stars is stopped in massive galaxies with the terminationof gas cooling and these galaxies soon become red with color $R-K>$5 (Vegamagnitude), comparable to the Extremely Red Objects (EROs) observed at redshift$z\sim$1-2. Still the predicted number density of very EROs is lower thanobserved at $z\sim 2$, and it may be related to inadequate descriptions of dustextinction, star formation history and AGN feedback in those luminous galaxies.Comment: Accepted for Publication in ApJ, added reference