Issue |
A&A
Volume 658, February 2022
|
|
---|---|---|
Article Number | A175 | |
Number of page(s) | 16 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/202142059 | |
Published online | 18 February 2022 |
XXL-HSC: An updated catalogue of high-redshift (z ≥ 3.5) X-ray AGN in the XMM-XXL northern field
Constraints on the bright end of the soft log N-log S⋆
1
IAASARS, National Observatory of Athens, Ioannou Metaxa and Vasileos Pavlou, 15236 Athens, Greece
e-mail: epouliasis@noa.gr
2
INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
3
Astronomical Institute, Tohoku University, 6-3 Aramaki, Aoba-ku, Senda 980-8578, Japan
4
Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
5
INAF, IASF Milano, via Corti 12, Milano 20133, Italy
6
AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, 91191 Gif-sur-Yvette, France
7
Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
8
Research Center for Space and Cosmic Evolution, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan
9
Department of Astronomy, University of Geneva, Ch. d’Écogia 16, 1290 Versoix, Switzerland
10
Academia Sinica Institute of Astronomy and Astrophysics, 11F of Astronomy-Mathematics Building, AS/NTU, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan
11
Universití di Bologna, Dip. di Fisica e Astronomia “A. Righi”, Via P. Gobetti 93/2, 40129 Bologna, Italy
Received:
20
August
2021
Accepted:
8
November
2021
X-rays offer a reliable method to identify active galactic nuclei (AGNs). However, in the high-redshift Universe, X-ray AGNs are poorly sampled due to their relatively low space density and the small areas covered by X-ray surveys. In addition to wide-area X-ray surveys, it is important to have deep optical data in order to locate the optical counterparts and determine their redshifts. In this work, we built a high-redshift (z ≥ 3.5) X-ray-selected AGN sample in the XMM-XXL northern field using the most updated [0.5–2 keV] catalogue along with a plethora of new spectroscopic and multi-wavelength catalogues, including the deep optical Subaru Hyper Suprime-Cam (HSC) data, reaching magnitude limits i ∼ 26 mag. We selected all the spectroscopically confirmed AGN and complement this sample with high-redshift candidates that are HSC g- and r-band dropouts. To confirm the dropouts, we derived their photometric redshifts using spectral energy distribution techniques. We obtained a sample of 54 high-z sources (28 with spec-z), the largest in this field so far (almost three times larger than in previous studies), and we estimated the possible contamination and completeness. We calculated the number counts (log N-log S) in different redshift bins and compared our results with previous studies and models. We provide the strongest high-redshift AGN constraints yet at bright fluxes (f0.5 − 2 keV > 10−15 erg s−1 cm−2). The samples of z ≥ 3.5, z ≥ 4, and z ≥ 5 are in agreement with an exponential decline model similar to that witnessed at optical wavelengths. Our work emphasises the importance of using wide-area X-ray surveys with deep optical data to uncover high-redshift AGNs.
Key words: galaxies: active / X-rays: galaxies / methods: data analysis / methods: observational / methods: statistical / early Universe
© ESO 2022
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