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[Mh/(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....
Plionis, M., Koutoulidis, L., Koulouridis, E., Moscardini, L., Lidman, C., Pierre, M., Adami, C., Chiappetti, L., Faccioli, L., Fotopoulou, S., Pacaud, F., & Paltani, S. (2018). The XXL Survey. XXXII. Spatial clustering of the XXL-S AGN. Astronomy and Astrophysics. https://doi.org/10.1051/0004-6361/201832970