Quasar clustering in a semi-analytic model based on ultra high-resolution N-body simulation

Taira Oogi

We investigate clustering properties of quasars using a new version of our semi-analytic model of galaxy and quasar formation with state-of-the-art cosmological N-body simulations.We assume that a major merger of galaxies triggers quasar activity. We find that the median mass of quasar host dark matter haloes increases with cosmic time by an order of magnitudefrom z=4 (a few 10^11 Msun) to z=1 (a few 10^12 Msun), and depends only weakly on the quasar luminosity. We also find that the quasar bias does not depend significantly on the quasar luminosity, similar to observed trends. This result reflects the fact that quasars with a fixed luminosity have various Eddington ratios and thus have various hot halo masses that primarily determine the quasar bias. The quasar bias increases with redshift, which is in qualitative agreement with observations. Our bias value is lower than the observed values at high redshifts, implying that we need some mechanisms that make quasars inactive in low-mass haloes and/or that make them more active in high-mass haloes.