Angular and spatial clustering of photometrically classified quasar candidates from SDSS NBCKDE

The present paper analyses the quasar clustering using the two-point correlation function (2pCF) and the largest existing sample of photometrically selected quasars: the SDSS NBCKDE catalogue (from the SDSS DR6). A new technique of random catalogue generation was developed for this purpose, that allows to take into account the original homogeneity of the survey without knowledge of its imaging mask. When averaged over photometrical redshifts 0.8<z_phot<2.2 the 2pCF of photometrically selected quasars is found to be approximated well with the power law w(theta)=(theta/theta_0)^{-alpha} with theta_0=4.5+/-1.4, alpha=0.94+/-0.06 over the range 1<theta<40. It agrees well with previous results by Myers et al. (2006,2007), obtained for samples of NBCKDE quasars with similar mean z_phot, but averaged over broader z_phot range. The parameters of the deprojected 2pCF averaged over the same z_phot range and modelled with a power law xi(r)=(r/r_0)^{-gamma}, are r_0=7.81^{+1.18}_{-1.16} Mpc/h, gamma=1.94+/-0.06, which are in perfect agreement with previous results from spectroscopic surveys. We confirm the evidence for an increase of the clustering amplitude with z, and find no evidence for luminosity dependence of the quasar clustering. The latter is consistent with the models of the quasar formation, in which bright and faint quasars are assumed to be similar sources, hosted by dark matter halos of similar masses, but observed at different stages of their evolution. Comparison of our results with studies of the X-ray selected AGNs with similar z shows that the clustering amplitude of optically selected quasars is similar to that of X-ray selected quasars, but lower than that of samples of all X-ray selected AGNs. As the samples of all X-ray selected AGNs contain AGNs of both types, our result serves as an evidence for different types of AGNs to reside in different environments.

Correlation function of quasars in real and redshift space from the Sloan Digital Sky Survey Data Release 7

We analyze the quasar two-point correlation function (2pCF) within the redshift interval $0.8<z<2.2$ using a sample of 52303 quasars selected from the recent 7th Data Release of the Sloan Digital Sky Survey. Our approach to 2pCF uses a concept of locally Lorentz (Fermi) frame for determination of the distance between objects and permutation method of the random catalogue generation. Assuming the spatially flat cosmological model with given $Omega_{Lambda}=0.726$, we found that the real-space 2pCF is fitted well with the power-low model within the distance range $1<sigma<35$ $h^{-1}$ Mpc with the correlation length $r_{0}=5.85pm0.33$ $h^{-1}$ Mpc and the slope $gamma=1.87pm0.07$. The redshift-space 2pCF is approximated with $s_{0}=6.43pm0.63$ $h^{-1}$ Mpc and $gamma=1.21pm0.24$ for $1<s<10$ $h^{-1}$ Mpc, and $s_{0}=7.37pm0.81$ $h^{-1}$ Mpc and $gamma=1.90pm0.24$ for $10<s<35$ $h^{-1}$ Mpc. For distances $s>10,h^{-1}$ Mpc the parameter describing the large-scale infall to density inhomogeneities is $beta=0.63pm0.10$ with the linear bias $b=1.44pm0.22$ that marginally (within 2$sigma$) agrees with the linear theory of cosmological perturbations. We discuss possibilities to obtain a statistical estimate of the random component of quasars velocities (different from the large-scale infall). We note rather slight dependence of quasars velocity dispersion upon the 2pCF parameters in the region $r<2$ Mpc.