Angular correlation functions of X-ray point-like sources in the full exposure XMM-LSS field

Aims: Our aim is to study the large-scale structure of different types of AGN using the medium-deep XMM-LSS survey.
Methods: We measure the two-point angular correlation function of 5700 and 2500 X-ray point-like sources over the 11 sq. deg. XMM-LSS field in the soft (0.5-2 keV) and hard (2-10 keV) bands. For the conversion from the angular to the spatial correlation function we used the Limber integral equation and the luminosity-dependent density evolution model of the AGN X-ray luminosity function.
Results: We have found significant angular correlations with the power-law parameters γ = 1.81 ± 0.02, θ₀ = 1.3'' ± 0.2'' for the soft, and γ = 2.00 ± 0.04, θ₀ = 7.3'' ± 1.0'' for the hard bands. The amplitude of the correlation function w(θ) is higher in the hard than in the soft band for f_x ≲ 10^-14 erg s^-1 cm^-2 and lower above this flux limit. We confirm that the clustering strength θ₀ grows with the flux limit of the sample, a trend which is also present in the amplitude of the spatial correlation function, but only for the soft band. In the hard band, it remains almost constant with r₀ ≃ 10h^-1 Mpc, irrespective of the flux limit. Our analysis of AGN subsamples with different hardness ratios shows that the sources with a hard-spectrum are more clustered than soft-spectrum ones. This result may be a hint that the two main types of AGN populate different environments. Finally, we find that our clustering results correspond to an X-ray selected AGN bias factor of 2.5 for the soft band sources (at a median bar{z} ≃ 1.1) and 3.3 for the hard band sources (at a median bar{z} ≃ 1), which translates into a host dark matter halo mass of 10¹³h^-1M_⊙ and 10^13.7h^-1M_⊙ for the soft and hard bands, respectively.

This paper is dedicated to the memory of Olivier Garcet who has initiated the present work just before his sudden death.