We present an estimate of the projected two-point correlation function (2PCF) of quasars in the Sloan Digital Sky Survey (SDSS) over the full range of one-and two-halo scales, 0.02 h −1 Mpc < r p < 120 h −1 Mpc. This was achieved by combining data from SDSS DR7 on large scales and Hennawi et al. (2006, with appropriate statistical corrections) on small scales. Our combined clustering sample is the largest spectroscopic quasar clustering sample to date, containing ∼ 48, 000 quasars in the redshift range 0.4 z 2.5 with median redshift 1.4. We interpret these precise 2PCF measurements within the halo occupation distribution (HOD) framework and constrain the occupation functions of central and satellite quasars in dark matter halos. In order to explain the small-scale clustering, the HOD modeling requires that a small fraction of z ∼ 1.4 quasars, f sat = (7.4 ± 1.4) × 10 −4 , be satellites in dark matter halos. At z ∼ 1.4, the median masses of the host halos of central and satellite quasars are constrained to be M cen = 4.1 +0.3 −0.4 × 10 12 h −1 M ⊙ and M sat = 3.6 +0.8 −1.0 × 10 14 h −1 M ⊙ , respectively. To investigate the redshift evolution of the quasar-halo relationship, we also perform HOD modeling of the projected 2PCF measured by Shen et al. (2007) for SDSS quasars with median redshift 3.2. We find tentative evidence for an increase in the mass scale of quasar host halos-the inferred median mass of halos hosting central quasars at z ∼ 3.2 is M cen = 14.1 +5.8 −6.9 × 10 12 h −1 M ⊙ . The cutoff profiles of the mean occupation functions of central quasars reveal that quasar luminosity is more tightly correlated with halo mass at higher redshifts. The average quasar duty cycle around the median host halo mass is inferred to be f q = 7.3 +0.6 −1.5 × 10 −4 at z ∼ 1.4 and f q = 8.6 +20.4 −7.2 × 10 −2 at z ∼ 3.2. We discuss the implications of our results for quasar evolution and quasar-galaxy co-evolution. Subject headings: galaxies: nuclei -quasars: general -large-scale structure of universe -dark matter

Using a fully cosmological hydrodynamic simulation that self‐consistently incorporates the growth and feedback of supermassive black holes and the physics of galaxy formation, we examine the effects of environmental factors (e.g. local gas density and black hole feedback) on the halo occupation distribution of low‐luminosity active galactic nuclei (AGN). We decompose the mean occupation function into central and satellite contribution and compute the conditional luminosity functions (CLFs). The CLF of the central AGN follows a lognormal distribution with the mean increasing and scatter decreasing with increasing redshifts. We analyse the light curves of individual AGN and show that the peak luminosity of the AGN has a tighter correlation with halo mass compared to instantaneous luminosity. We also compute the CLF of satellite AGN at a given central AGN luminosity. We do not see any significant correlation between the number of satellites with the luminosity of the central AGN at a fixed halo mass. We also show that for a sample of AGN with luminosity above 1042 erg s−1 the mean occupation function can be modelled as a softened step function for central AGN and a power law for the satellite population. The radial distribution of AGN inside haloes follows a power law at all redshifts with a mean index of −2.33 ± 0.08. Incorporating the environmental dependence of supermassive black hole accretion and feedback, our formalism provides a theoretical tool for interpreting current and future measurements of AGN clustering.

We perform halo occupation distribution (HOD) modeling of the projected two-point correlation function (2PCF) of high-redshift (z ∼ 1.2) X-ray-bright active galactic nuclei (AGN) in the XMM-COSMOS field measured by Allevato et al. The HOD parameterization is based on low-luminosity AGN in cosmological simulations. At the median redshift of z ∼ 1.2, we derive a median mass of 1.02 +0.21 −0.23 × 10 13 h −1 M ⊙ for halos hosting central AGN and an upper limit of ∼ 10% on the AGN satellite fraction. Our modeling results indicate (at the 2.5σ level) that X-ray AGN reside in more massive halos compared to more bolometrically luminous, optically-selected quasars at similar redshift. The modeling also yields constraints on the duty cycle of the X-ray AGN, and we find that at z ∼ 1.2 the average duration of the X-ray AGN phase is two orders of magnitude longer than that of the quasar phase. Our inferred mean occupation function of X-ray AGN is similar to recent empirical measurements with a group catalog and suggests that AGN halo occupancy increases with increasing halo mass. We project the XMM-COSMOS 2PCF measurements to forecast the required survey parameters needed in future AGN clustering studies to enable higher precision HOD constraints and determinations of key physical parameters like the satellite fraction and duty cycle. We find that N 2 /A ∼ 5 × 10 6 deg −2 (with N the number of AGN in a survey area of A deg 2 ) is sufficient to constrain the HOD parameters at the 10% level, which is easily achievable by upcoming and proposed X-ray surveys.