Spatial Correlation Function of theChandra‐selected Active Galactic Nuclei

Abstract

We present the spatial correlation function of nonstellar X-ray point sources in the 0.4 deg-2 Chandra Large Area Synoptic X-Ray Survey (CLASXS) using 233 spectroscopically identified sources. We supplement our analysis with 252 sources with redshifts from the Chandra Deep Field-North (CDF-N), allowing correlation functions that have been estimated over comoving scales of a few to a few hundred Mpc. We calculate both redshift-space and projected correlation functions, averaged over the redshift range of 0.1 < z < 3.0, for both CLASXS and CDF-N fields. The correlation functions can be described well with a power law in the form ξ(s) = (s/s0)-γ, with γ = 1.6 and s0 = 8.0 Mpc for the CLASXS field and s0 = 8.55 Mpc and γ = 1.3 ± 0.1 for the CDF-N field. The real-space correlation functions derived from the projected correlation functions are found to be r0 = 8.1 Mpc and γ = 2.1 ± 0.5 for the CLASXS field and r0 = 5.8 Mpc and γ = 1.38 for the CDF-N field. By comparing the real- and redshift-space correlation functions in the combined CLASXS and CDFN samples, we are able to estimate the redshift distortion parameter β = 0.4 ± 0.2 at an effective redshift z = 0.94. We find a weak correlation between X-ray luminosity and clustering amplitude. We study the evolution of the AGN clustering by dividing the samples into four redshift bins over 0.1 Mpc < z < 3.0 Mpc. We find a mild evolution in the clustering amplitude, corresponding to a rapid increase of bias with redshift [b(z = 0.45) = 0.95 ± 0.15 and b(z = 2.07) = 3.03 ± 0.83], similar to that found in optically selected quasars. The average halo mass is found to be log(Mhalo/M☉) ~ 12.1.