The XXL Survey
XXI. The environment and clustering of X-ray AGN in the XXL-South field
Department of Physics, Faculty of Science, University of Zagreb,
Bijenička cesta 32,
2 Main Astronomical Observatory, Academy of Sciences of Ukraine, 27 Akademika Zabolotnoho St., 03680 Kyiv, Ukraine
3 Physics Dept., Aristotle Univ. of Thessaloniki, Thessaloniki 54124, Greece
4 Instituto Nacional de Astrófisica, Óptica y Electrónica, 72000 Puebla, Mexico
5 IAASARS, National Observatory of Athens, 15236 Penteli, Greece
6 DSM/Irfu/SAp, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France
7 Department of Astronomy, University of Geneva, ch. d’Ecogia 16, 1290 Versoix, Switzerland
8 INAF-IASF Milano, via Bassini 15, 20133 Milano, Italy
9 Aix Marseille Univ., CNRS, CNES, LAM, Marseille, France
10 International Centre for Radio Astronomy Research, M468, University of Western Australia, Crawley, WA 6009, Australia
11 Subaru Telescope, National Astronomical Observatory of Japan, 650 North Aohoku Place, Hilo, HI 96720, USA
12 Australian Astronomical Observatory, North Ryde, NSW 2113, Australia
13 European Southern Observatory, Alonso de Cordova 3107, Vitacura, 19001 Casilla, Santiago 19, Chile
14 Dipartimento di Fisica e Astronomia, Alma Mater Studiorum, Università degli Studi di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
15 INAF – Osservatorio Astronomico di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
16 Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 19c, 4000 Liège, Belgium
Accepted: 22 November 2017
Context. This work is part of a series of studies focusing on the environment and the properties of the X-ray selected active galactic nuclei (AGN) population from the XXL survey. The present survey, given its large area, continuity, extensive multiwavelength coverage, and large-scale structure information, is ideal for this kind of study. Here, we focus on the XXL-South (XXL-S) field.
Aims. Our main aim is to study the environment of the various types of X-ray selected AGN and investigate its possible role in AGN triggering and evolution.
Methods. We studied the large-scale (>1 Mpc) environment up to redshift z = 1 using the nearest neighbour distance method to compare various pairs of AGN types. We also investigated the small-scale environment (<0.4 Mpc) by calculating the local overdensities of optical galaxies. In addition, we built a catalogue of AGN concentrations with two or more members using the hierarchical clustering method and we correlated them with the X-ray galaxy clusters detected in the XXL survey.
Results. It is found that radio detected X-ray sources are more obscured than non-radio ones, though not all radio sources are obscured AGN. We did not find any significant differences in the large-scale clustering between luminous and faint X-ray AGN, or between obscured and unobscured ones, or between radio and non-radio sources. At local scales (<0.4 Mpc), AGN typically reside in overdense regions, compared to non-AGN; however, no differences were found between the various types of AGN. A majority of AGN concentrations with two or more members are found in the neighbourhood of X-ray galaxy clusters within <25–45 Mpc. Our results suggest that X-ray AGN are typically located in supercluster filaments, but they are also found in over- and underdense regions.
Key words: X-rays: galaxies: clusters / galaxies: active / radio continuum: galaxies / quasars: general
© ESO 2018