Clustering analyses of 300,000 photometrically classified quasars. I. Luminosity and redshift evolution in quasar bias

Adam D. Myers, Robert J. Brunner, Robert C. Nichol, Gordon T. Richards, Donald P. Schneider, Neta A. Bahcall

Research output: Contribution to journalArticlepeer-review

152 Scopus citations


Using ∼300,000 photometrically classified quasars, by far the largest quasar sample ever used for such analyses, we study the redshift and luminosity evolution of quasar clustering on scales of ∼50 h-1 kpc to ∼20 h-1 Mpc from redshifts of z̄ ∼ 0.75-2.28. We parameterize our clustering amplitudes using realistic dark matter models and find that a ACDM power spectrum provides a superb fit to our data with a redshift-averaged quasar bias of bQz̄=1.40 = 2.41 ± 0.08 (P<χ2 = 0.847) for σ8 = 0.9. This represents a better fit than the best-fit power-law model [ω = (0.0493 ± 0.0064)θ-928±0-055; P <χ2 = 0.482]. We find bQ increases with redshift. This evolution is significant at >99.6% using our data set alone, increasing to >99.9999% if stellar contamination is not explicitly parameterized. We measure the quasar classification efficiency across our full sample as a = 95.6 ± 1.94.4%, a star-quasar separation comparable to the star-galaxy separation in many photometric studies of galaxy clustering. We derive the mean mass of the dark matter halos hosting quasars as MDMH = (5.2 ± 0.6) × 1012 h-1 M. At z̄ ∼ 1.9 we find a 1.5 σ deviation from luminosity- independent quasar clustering; this suggests that increasing our sample size by a factor of ∼ 1.8 could begin to constrain any luminosity dependence in quasar bias at z ∼ 2. Our results agree with recent studies of quasar environments at z < 0.4, which detected little luminosity dependence to quasar clustering on proper scales ≳50 h-1 kpc. At z < 1.6, our analysis suggests that bQ is constant with luminosity to within ΔbQ ∼ 0.6, and that, for g < 21, angular quasar autocorrelation measurements are unlikely to have sufficient statistical power at z ≲ 1.6 to detect any luminosity dependence in quasars' clustering.

Original languageEnglish (US)
Pages (from-to)85-98
Number of pages14
JournalAstrophysical Journal
Issue number1 I
StatePublished - Mar 20 2007

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Cosmology: observations
  • Large-scale structure of universe
  • Quasars: general
  • Surveys


Dive into the research topics of 'Clustering analyses of 300,000 photometrically classified quasars. I. Luminosity and redshift evolution in quasar bias'. Together they form a unique fingerprint.

Cite this