Binary Quasars at High Redshift. II. Sub-Mpc Clustering at z ~ 3-4

The Astrophysical Journal (Impact Factor: 6.28). 08/2010; 719(2):1693. DOI: 10.1088/0004-637X/719/2/1693
Source: arXiv

ABSTRACT We present measurements of the small-scale (0.1 r 1 h –1 Mpc) quasar two-point correlation function at z>2.9, for a flux-limited (i < 21) sample of 15 binary quasars compiled by Hennawi et al. The amplitude of the small-scale clustering increases from z ~ 3 to z ~ 4. The small-scale clustering amplitude is comparable to or lower than power-law extrapolations (assuming a fixed slope γ = 2) from the large-scale correlation function of the i < 20.2 quasar sample from the Sloan Digital Sky Survey. Using simple prescriptions relating quasars to dark matter halos, we model the observed small-scale clustering with halo occupation models. We found that the level of small-scale clustering favors an active fraction of black holes in (M 1013 h –1 M ☉) satellite halos fs 0.1 at z 3.

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    ABSTRACT: With close pairs of quasars at different redshifts, a background quasar sightline can be used to study a foreground quasar's environment in absorption. We use a sample of 650 projected quasar pairs to study the HI Lya absorption transverse to luminous, z~2 quasars at proper separations of 30kpc < R < 1Mpc. In contrast to measurements along the line-of-sight, regions transverse to quasars exhibit enhanced HI Lya absorption and a larger variance than the ambient intergalactic medium, with increasing absorption and variance toward smaller scales. Analysis of composite spectra reveals excess absorption characterized by a Lya equivalent width profile W = 2.3A (R/100kpc)^-0.46. We also observe a high (~60%) covering factor of strong, optically thick HI absorbers (HI column log NHI > 17.3) at separations R<200kpc, which decreases to ~20% at R~1Mpc, but still represents a significant excess over the cosmic average. This excess of optically thick absorption can be described by a quasar-absorber cross-correlation function xi_QA(r) = (r/r_0)^gamma with a large correlation length r_0 = 12.5+2.7-1.4 Mpc/h (comoving) and gamma = 1.68+0.14-0.30. The HI absorption measured around quasars exceeds that of any previously studied population, consistent with quasars being hosted by massive dark matter halos Mhalo~10^12.5 Msun at z~2.5. The environments of these massive halos are highly biased towards producing optically thick gas, and may even dominate the cosmic abundance of Lyman limit systems and hence the intergalactic opacity to ionizing photons at z~2.5. The anisotropic absorption around quasars implies the transverse direction is much less likely to be illuminated by ionizing radiation than the line-of-sight, which we interpret in terms of the same obscuration effects frequently invoked in unified models of active galactic nuclei.
    The Astrophysical Journal 08/2013; 776(2). · 6.28 Impact Factor
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    ABSTRACT: Kiloparsec-scale binary active galactic nuclei (AGNs) signal active supermassive black hole (SMBH) pairs in merging galaxies. Despite their significance, unambiguously confirmed cases remain scarce and most have been discovered serendipitously. In a previous systematic search, we optically identified four kpc-scale binary AGNs from candidates selected with double-peaked narrow emission lines at z = 0.1-0.2. Here, we present Chandra and Hubble Space Telescope Wide Field Camera 3 (WFC3) imaging of these four systems. We critically examine and confirm the binary-AGN scenario for two of the four targets, by combining high angular resolution X-ray imaging spectroscopy with Chandra ACIS-S, better nuclear position constraints from WFC3 F105W imaging, and direct starburst estimates from WFC3 F336W imaging; for the other two targets, the existing data are still consistent with the binary-AGN scenario, but we cannot rule out the possibility of only one AGN ionizing gas in both merging galaxies. We find tentative evidence for a systematically smaller X-ray-to-[O III] luminosity ratio and/or higher Compton-thick fraction in optically selected kpc-scale binary AGNs than in single AGNs, possibly caused by a higher nuclear gas column due to mergers and/or a viewing angle bias related to the double-peak narrow-line selection. While our result lends some further support to the general approach of optically identifying kpc-scale binary AGNs, it also highlights the challenge and ambiguity of X-ray confirmation.
    The Astrophysical Journal 12/2012; 762(2):110. · 6.28 Impact Factor
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    ABSTRACT: Recent work on quasar clustering suggests a degeneracy in the halo occupation distribution constrained from two-point correlation functions. To break this degeneracy, we make the first empirical measurement of the mean occupation function (MOF) of quasars at z ~ 0.2 by matching quasar positions with groups and clusters identified in the MaxBCG sample. We fit two models to the MOF, a power law and a 4-parameter model. The number distribution of quasars in host halos is close to Poisson, and the slopes of the MOF obtained from our best-fit models (for the power law case) favor a MOF that monotonically increases with halo mass. The best-fit slopes are 0.53 +/- 0.04 and 1.03 +/- 1.12 for the power law model and the 4-parameter model, respectively. We measure the radial distribution of quasars within dark matter halos and find it to be adequately described by a power law with a slope -2.3 +/- 0.4. We measure the conditional luminosity function (CLF) of quasars and show that there is no evidence of luminosity evolution of quasars with host halo mass, similar to the inferences drawn from clustering measurements. We also measure the conditional black hole mass function (CMF) of our quasars. Although the results are consistent with no evolution, we observe a slight indication of downsizing of the black hole mass function. The lack of evolution in the CLF and the CMF shows that quasars, residing in clusters have a characteristic mass and luminosity scale independent of their host halos.
    The Astrophysical Journal 09/2013; 779(2). · 6.28 Impact Factor

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