Relations between Galaxy Formation and the Environments of Quasars

We investigate the environments of quasars using a semi-analytic model which includes both galaxy and quasar formations based on a hierarchical clustering scenario. We assume that a supermassive black hole is formed and fueled by the accretion of cold gas during a major merger of galaxies. Our model can reproduce not only the general form of the galaxy luminosity functions in the local Universe, but also the observed relation between a supermassive black hole mass and a spheroid luminosity, the present black hole mass function and the quasar luminosity functions at different redshifts. Using this model, we predict the mean number of quasars per halo, the bias parameter of quasars and the probability distribution of the number of galaxies around quasars. The results of our model show that the spatial distribution of galaxies is different from that of quasars. Furthermore, we found that at 0.2 z 0.5 most quasars are likely to reside in galaxy groups. On the other hand, at 1 z 2 most quasars seem to reside in environments ranging from small groups of galaxies to clusters of galaxies. Comparing these predictions with observations in the future will enable us to constrain our model of quasar formation.