A. Elyiv, N. Clerc, M. Plionis, J. Surdej, M. Pierre, S. Basilakos, L. Chiappetti, P. Gandhi, E. Gosset, O. Melnyk, F. Pacaud
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 (0.5-2 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. We have found significant angular
correlations with the power-law parameters gamma = 1.81 +/- 0.02, theta_0 =
1.3" +/- 0.2" for the soft, and gamma = 2.00 +/- 0.04, theta_0 = 7.3" +/- 1.0"
for the hard bands. The amplitude of the correlation function w(theta) 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 theta_0
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 r_0 = 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 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 ~ 10^13 h^-1 M_o
and ~ 10^13.7 h^-1 M_o for the soft and hard bands, respectively.
View original:
http://arxiv.org/abs/1111.5982
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