The XXL Survey

XXXII. Spatial clustering of the XXL-S AGN^★

¹ National Observatory of Athens, Lofos Nymfon, Thession, Athens 11810, Greece
e-mail: mplionis@physics.auth.gr
² Physics Department, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
³ AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, 91191 Gif-sur-Yvette, France
⁴ Dipartimento di Fisica e Astronomia, Alma Mater Studiorum Università di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
⁵ INAF - Osservatorio di Astrofisica e Scienza dello Spazio, via Gobetti 93/3, 40129 Bologna, Italy
⁶ INFN, Sezione di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
⁷ Australian Astronomical Observatory, PO Box 915, North Ryde NSW 1670, Australia
⁸ LAM, OAMP, Université Aix-Marseille, CNRS, Pôle de l’Étoile, Site de Chãteau Gombert, 38 rue Frédéric Joliot-Curie, 13388 Marseille 13 Cedex, France
⁹ INAF - IASF - Milano, Via Bassini 15, 20133 Milano, Italy
¹⁰ Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK
¹¹ Argelander Institut fuer Astronomie, Universitaet Bonn, Auf dem Huegel 71, 53121 Bonn, Germany
¹² Department of Astronomy, University of Geneva, ch. d’Ecogia 16, 1290 Versoix, Switzerland

Received: 6 March 2018
Accepted: 9 April 2018

Abstract

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.