The 2dF QSO Redshift Survey - XIV. Structure and evolution from the two-point correlation function

Abstract

In this paper we present a clustering analysis of quasi‐stellar objects (QSOs) using over 20 000 objects from the final catalogue of the 2dF QSO Redshift Survey (2QZ), measuring the redshift‐space two‐point correlation function, ξ(s). When averaged over the redshift range 0.3 < z < 2.2 we find that ξ(s) is flat on small scales, steepening on scales above ∼25 h−1 Mpc. In a WMAP/2dF cosmology (Ωm= 0.27, ΩΛ= 0.73) we find a best‐fitting power law with s0= 5.48+0.42−0.48 h−1 Mpc and γ= 1.20 ± 0.10 on scales s= 1 to 25 h−1 Mpc. We demonstrate that non‐linear redshift‐space distortions have a significant effect on the QSO ξ(s) at scales less than ∼10 h−1 Mpc. A cold dark matter model assuming WMAP/2dF cosmological parameters is a good description of the QSO ξ(s) after accounting for non‐linear clustering and redshift‐space distortions, and allowing for a linear bias at the mean redshift of bQ(z= 1.35) = 2.02 ± 0.07. We subdivide the 2QZ into 10 redshift intervals with effective redshifts from z= 0.53 to 2.48. We find a significant increase in clustering amplitude at high redshift in the WMAP/2dF cosmology. The QSO clustering amplitude increases with redshift such that the integrated correlation function, , within 20 h−1 Mpc is and . We derive the QSO bias and find it to be a strong function of redshift with bQ(z= 0.53) = 1.13 ± 0.18 and bQ(z= 2.48) = 4.24 ± 0.53. We use these bias values to derive the mean dark matter halo (DMH) mass occupied by the QSOs. At all redshifts 2QZ QSOs inhabit approximately the same mass DMHs with MDH= (3.0 ± 1.6) × 1012 h−1 M⊙, which is close to the characteristic mass in the Press–Schechter mass function, M*, at z= 0. These results imply that L*Q QSOs at z∼ 0 should be largely unbiased. If the relation between black hole (BH) mass and MDH or host velocity dispersion does not evolve, then we find that the accretion efficiency (L/LEdd) for L*Q QSOs is approximately constant with redshift. Thus the fading of the QSO population from z∼ 2 to ∼0 appears to be due to less massive BHs being active at low redshift. We apply different methods to estimate, tQ, the active lifetime of QSOs and constrain tQ to be in the range 4 × 106–6 × 108 yr at z∼ 2. We test for any luminosity dependence of QSO clustering by measuring ξ(s) as a function of apparent magnitude (equivalent to luminosity relative to L*Q). However, we find no significant evidence of luminosity‐dependent clustering from this data set.

High-precision multi-band measurements of the angular clustering of X-ray sources

“…Similar results for b 0 were obtained by Basilakos et al (2005), who also studied the bias evolution for both clustering models. Gilli et al (2009) found b 0 values in the range 1.5-2, similar to that of Croom et al (2005), consistent with our predictions for a = −3 clustering scenario.…”

“…In general, X-ray selected AGN show larger bias parameters than optically selected AGN (e.g. Croom et al 2005;Myers et al 2007). This could mean that the underlying matter distribution is traced differently in Xrays and in the optical domain, with X-ray selected AGN residing in more massive DMH than the optically selected AGN.…”

“…This could mean that the underlying matter distribution is traced differently in Xrays and in the optical domain, with X-ray selected AGN residing in more massive DMH than the optically selected AGN. A number of works (Porciani et al 2004;Croom et al 2005;Basilakos et al 2008) show that optical AGN are likely to be hosted by DMH with masses 10 −13 h −1 M , while X-ray AGN are usually embedded in DMH with masses 10 −13 h −1 M . Our results, however, are slightly lower but consistent nevertheless with the estimations from the spatial clustering of COSMOS sources (M DMH ∼ 12.4−12.8 h −1 M , Gilli et al 2009).…”

Dusty star-forming galaxies at high redshift

“…Brodwin et al (2008) found that DOGs selected above a 24 µm flux density S 24 > 0.3 mJy have r 0 = 7.4h −1 Mpc, quite similar to the Hickox et al (2012) autocorrelation length of SMGs of r 0 = 7.7h −1 Mpc. The inferred halo masses for luminous SMGs and DOGs are not terribly dissimilar from constraints on optically-selected quasars (Croom et al, 2005;White et al, 2012).…”

The QSO Luminosity Function from the 2dF QSO Redshift Survey and the Associated 6dF QSO Redshift Survey at 0.3 ≤ z ≤ 2.4

“…The total survey area is 721.6 deg 2 , when allowance is made for regions of sky excised around the bright stars. The QSO candidates for the 2QZ (18.25 < b J < 20.85) were selected based on fulfilling at least one of the following colour criteria: [7,18,19] and for the 6QZ (16.0 < b J < 18.25) the colour criteria is u − b J ≤ −0.50 [18,23]. The data from both the 2dF and 6dF were reduced using the pipeline data reduction system 2DFDR [24].…”