XXL-HSC: An updated catalogue of high-redshift (z ≥ 3.5) X-ray AGN in the XMM-XXL northern field

Journal Article · 17 February 2022 · Astronomy and Astrophysics

DOI: https://doi.org/10.1051/0004-6361/202142059 · OSTI ID:1982304

Pouliasis, E.  ^[1]; Georgantopoulos, I. ^[1]; Ruiz, A. ^[1]; Gilli, R. ^[2]; Koulouridis, E. ^[1]; Akiyama, M. ^[3]; Ueda, Y. ^[4]; Chiappetti, L. ^[2]; Garrel, C. ^[5]; Horellou, C. ^[6]; Nagao, T. ^[7]; Paltani, S. ^[8]; Pierre, M. ^[5]; Toba, Y. ^[9]; Vignali, C. ^[10]

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1. National Observatory of Athens (Greece)
2. Istituto Nazionale di Astrofisica (INAF) (Italy)
3. Tohoku Univ., Sendai (Japan)
4. Kyoto Univ. (Japan)
5. Centre National de la Recherche Scientifique (CNRS) (France); Commissariat a l'Energie Atomique (CEA) (France); Univ. Paris-Saclay, Gif-sur-Yvette (France); University Paris-Diderot (France)
6. Chalmers University of Technology (Sweden)
7. Ehime Univ., Matsuyama (Japan)
8. Univ. of Geneva (Switzerland)
9. Kyoto Univ. (Japan); Ehime Univ., Matsuyama (Japan); Academia Sinica, Taipei (Taiwan)
10. Univ. of Bologna (Italy); Istituto Nazionale di Astrofisica (INAF) (Italy)

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. Here, 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 (f_{0.5 – 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.

• Research Organization: US Department of Energy (USDOE), Washington, DC (United States). Office of Science, Sloan Digital Sky Survey (SDSS)
• Sponsoring Organization: USDOE Office of Science (SC); Alfred P. Sloan Foundation
• OSTI ID: 1982304
• Journal Information: Astronomy and Astrophysics, Journal Name: Astronomy and Astrophysics Vol. 658; ISSN 0004-6361
• Publisher: EDP SciencesCopyright Statement
• Country of Publication: United States
• Language: English