SIMBAD references

Our aim is to study the large-scale structure of different types of AGN using the medium-deep XMM-LSS survey. 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 (0.5-2keV) and hard (2-10keV) 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. 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^–14erg/s/cm2 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^–1Mpc, 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 z≃1.1) and ∼3.3 for the hard band sources (at a median 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.