Halo Occupation Distribution of Infrared Selected Quasars

TL;DR

This study models the distribution of infrared-selected quasars within dark matter halos using HOD analysis, revealing host mass scales and satellite fractions at redshift around 1, with implications for galaxy evolution theories.

Contribution

It provides the first detailed HOD modeling of WISE-selected quasars at z~1, highlighting differences in satellite fractions compared to previous SDSS-based studies.

Findings

Median host halo mass for central quasars: ~5 x 10^12 M_sun

Satellite fraction of quasars: ~0.005

Lower host mass scale for satellite quasars compared to previous studies

Abstract

We perform a Halo Occupation Distribution (HOD) modeling of the projected two-point correlation function (2PCF) of quasars that are observed in the Wide-field Infrared Survey Explorer (WISE) telescope with counter-parts in the Sloan Digital Sky Survey (SDSS) Data Release (DR)-8 quasar catalog at a median redshift of $z\sim 1.04 (\pm 0.58)$. Using a four parameter HOD model we derive the host mass scales of WISE selected quasars. Our results show that the median halo masses of central and satellite quasars lie in the range $M_{\mathrm{cen}} = (5 \pm 1.0) \times 10^{12} M_{\odot}$ and $M_{\mathrm{sat}} = 8 (^{+7.8} _{-4.8}) \times 10^{13} M_{\odot}$, respectively. The derived satellite fraction is $f_{\mathrm{sat}}= 5.5 (^{+35} _{-5.0})\times 10^{-3}$. Previously Richardson et al.\ used the SDSS DR7 quasar clustering data to obtain the halo mass distributions of $z\sim 1.4$ quasars. Our results on the HOD of central quasars are in excellent agreement with Richardson et al.\ but the host mass scale of satellite quasars for the WISE sample, is lower than that of Richardson et al.\ resulting in an order of magnitude higher satellite fraction for the WISE sample. We note that our sample of quasars are systematically brighter in the WISE frequency bands compared to the full quasar sample of SDSS. We discuss the implication of this result in the context of current theories of galaxy evolution.