Spatial correlation function of the Chandra-selected active galactic nuclei

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 xi(s) = (s/s(0))(-gamma), with gamma = 1.6(-0.3)(+0.4) and s(0) = 8.0(-1.5)(+1.4) Mpc for the CLASXS field and s(0) = 8.55(-0.74)(+0.75) Mpc and gamma = 1.3 +/- 0.1 for the CDF-N field. The real-space correlation functions derived from the projected correlation functions are found to be r(0) = 8.1(-2.2)(+1.2) Mpc and gamma = 2.1 +/- 0.5 for the CLASXS field and r(0) = 5.8(-1.5)(+1.0) Mpc and gamma = 1.38(-0.14)(+0.12) 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 beta = 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 (M-halo/M-circle dot) similar to 12.1.