The Sloan Digital Sky Survey Quasar Lens Search. V. Final Catalog from the Seventh Data Release

The Astronomical Journal (Impact Factor: 4.05). 04/2012; 143(5):119. DOI: 10.1088/0004-6256/143/5/119

ABSTRACT We present the final statistical sample of lensed quasars from the Sloan Digital Sky Survey (SDSS) Quasar Lens Search (SQLS). The well-defined statistical lens sample consists of 26 lensed quasars brighter than i = 19.1 and in the redshift range of 0.6 < z < 2.2 selected from 50,826 spectroscopically confirmed quasars in the SDSS Data Release 7 (DR7), where we restrict the image separation range to 1'' < θ < 20'' and the i-band magnitude differences in two images to be smaller than 1.25 mag. The SDSS DR7 quasar catalog also contains 36 additional lenses identified with various techniques. In addition to these lensed quasars, we have identified 81 pairs of quasars from follow-up spectroscopy, 26 of which are physically associated binary quasars. The statistical lens sample covers a wide range of image separations, redshifts, and magnitudes, and therefore is suitable for systematic studies of cosmological parameters and surveys of the structure and evolution of galaxies and quasars.

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    ABSTRACT: We measure the small-scale (comoving separation 10 kpc/h < r_p < 200 kpc/h) two-point correlation function of quasars using a sample of 26 spectroscopically confirmed binary quasars at 0.6<z<2.2 from the Sloan Digital Sky Survey Quasar Lens Search (SQLS). Thanks to careful candidate selections and extensive follow-up observations of the SQLS, which is aimed at constructing a complete quasar lens sample, our sample of binary quasars is also expected to be nearly complete within a specified range of angular separations and redshifts. The measured small-scale correlation function rises steeply toward smaller scales, which is consistent with earlier studies based on incomplete or smaller binary quasar samples. We find that the quasar correlation function can be fitted by a power-law reasonably well over 4 order of magnitudes, with the best-fit slope of xi(r)\propto r^{-1.92}. We interpret the measured correlation function within the framework of the Halo Occupation Distribution (HOD). We propose a simple model which assumes a constant fraction of quasars that appear as satellites in dark matter haloes, and find that measured small-scale clustering signals constrain the satellite fraction to f_sat=0.054_{-0.016}^{+0.017} for a singular isothermal sphere number density profile of satellites. We note that the HOD modelling appears to underpredict clustering signals at the smallest separations of r_p ~ 10 kpc/h unless we assume very steep number density profiles (such as an NFW profile with the concentration parameter c_vir > 30), which may be suggestive of enhanced quasar activities by direct interactions.
    Monthly Notices of the Royal Astronomical Society 03/2012; 424(2). DOI:10.1111/j.1365-2966.2012.21321.x · 5.23 Impact Factor
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    ABSTRACT: We present a statistical analysis of the final lens sample from the Sloan Digital Sky Survey Quasar Lens Search (SQLS). The number distribution of a complete subsample of 19 lensed quasars selected from 50,836 source quasars is compared with theoretical expectations, with particular attention given to the selection function. Assuming that the velocity function of galaxies does not evolve with redshift, the SQLS sample constrains the cosmological constant to ΩΛ = 0.79+0.06 –0.07(stat.)+0.06 –0.06(syst.) for a flat universe. The dark energy equation of state is found to be consistent with w = –1 when the SQLS is combined with constraints from baryon acoustic oscillation (BAO) measurements or results from the Wilkinson Microwave Anisotropy Probe (WMAP). We also obtain simultaneous constraints on cosmological parameters and redshift evolution of the galaxy velocity function, finding no evidence for redshift evolution at z 1 in any combinations of constraints. For instance, number density evolution quantified as ν n ≡ dln */dln (1 + z) and the velocity dispersion evolution νσ ≡ dln σ*/dln (1 + z) are constrained to ν n = 1.06+1.36 –1.39(stat.)+0.33 –0.64(syst.) and νσ = –0.05+0.19 –0.16(stat.)+0.03 –0.03(syst.), respectively, when the SQLS result is combined with BAO and WMAP for flat models with a cosmological constant. We find that a significant amount of dark energy is preferred even after fully marginalizing over the galaxy evolution parameters. Thus, the statistics of lensed quasars robustly confirm the accelerated cosmic expansion.
    The Astronomical Journal 04/2012; 143(5):120. DOI:10.1088/0004-6256/143/5/120 · 4.05 Impact Factor
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    ABSTRACT: We report the discovery of a pair of quasars at $z=1.487$, with a separation of $8\farcs585\pm0\farcs002$. Subaru Telescope infrared imaging reveals the presence of an elliptical and a disk-like galaxy located almost symmetrically between the quasars, creating a cross-like configuration. Based on absorption lines in the quasar spectra and the colors of the galaxies, we estimate that both galaxies are located at redshift $z=0.899$. This, as well as the similarity of the quasar spectra, suggests that the system is a single quasar multiply imaged by a galaxy group or cluster acting as a gravitational lens, although the possibility of a binary quasar cannot be fully excluded. We show that the gravitational lensing hypothesis implies these galaxies are not isolated, but must be embedded in a dark matter halo of virial mass $\sim 4 \times 10^{14}\ h_{70}^{-1}\ {M}_\odot$ assuming an NFW model with a concentration parameter of $c_{vir}=6$, or a singular isothermal sphere profile with a velocity dispersion of $\sim 670$ km s$^{-1}$. We place constraints on the location of the dark matter halo, as well as the velocity dispersions of the galaxies. In addition, we discuss the influence of differential reddening, microlensing and intrinsic variability on the quasar spectra and broadband photometry.
    The Astrophysical Journal 06/2012; 765(2). DOI:10.1088/0004-637X/765/2/139 · 6.28 Impact Factor
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