The XXL Survey. XXXII. Spatial clustering of the XXL-S AGN

The XMM-XXL Survey spans two fields of 25 deg² each observed for more than 6 Ms with XMM, which provided a sample of tens of thousands of point sources with a flux limit of 2.2 × 10^-15 and 1.4 × 10^-14 erg s^-1 cm², corresponding to 50% of the area curve, in the soft band (0.5-2 keV) and hard band (2-10 keV), respectively. In this paper we present the spatial clustering properties of 3100 and 1900 X-ray active galactic nuclei (AGNs) in the soft and hard bands, respectively, which have been spectroscopically observed with the AAOmega facility. This sample is 90% redshift complete down to an optical magnitude limit of r ≲ 21.8. The sources span the redshift interval 0 < z < 5.2, although in the current analysis we limit our samples to z ≤ 3, with corresponding sample median values of z̅ ≃ 0.96 and 0.79 for the soft band and hard band, respectively. We employ the projected two-point correlation function to infer the spatial clustering and find a correlation length r₀ = 7.0(±0.34) and 6.42(±0.42) h^-1 Mpc, respectively, for the soft- and hard-band detected sources with a slope for both cases of γ = 1.44(±0.1). The power-law clustering was detected within comoving separations of 1 and 25 h^-1 Mpc. These results, as well as those derived in two separate redshift ranges, provide bias factors of the corresponding AGN host dark matter halos that are consistent with a halo mass of log₁₀[M_h/(h^-1M_⊙)] = 13.04 ± 0.06, confirming the results of most recent studies based on smaller X-ray AGN samples.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.