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Compton-thick accretion in the local universe

Compton-thick accretion in the local universe
Compton-thick accretion in the local universe
Heavily obscured accretion is believed to represent an important stage in the growth of supermassive black holes and to play an important role in shaping the observed spectrum of the cosmic X-ray background. Hard X-ray (E > 10 keV) selected samples are less affected by absorption than samples selected at lower energies, and are therefore one of the best ways to detect and identify Compton-thick (CT, log NH ≥ 24) active galactic nuclei (AGNs). In this letter we present the first results of the largest broadband (0.3–150 keV) X-ray spectral study of hard X-ray selected AGNs to date, focusing on the properties of heavily obscured sources. Our sample includes the 834 AGNs (728 non-blazar, average redshift z sime 0.055) reported in the 70-month catalog of the all-sky hard X-ray Swift/Burst Alert Monitor survey. We find 55 CT AGNs, which represent 7.6-2.1+1.1 % of our non-blazar sample. Of these, 26 are reported as candidate CT AGNs for the first time. We correct for selection bias and derive the intrinsic column density distribution of AGNs in the local universe in two different luminosity ranges. We find a significant decrease in the fraction of obscured Compton-thin AGNs for increasing luminosity, from 46 ± 3% (for log L14-195 = 40–43.7) to 39 ± 3% (for log L14-195 = 43.7–46). A similar trend is also found for CT AGNs. The intrinsic fraction of CT AGNs with log NH = 24–25 normalized to unity in the NH = 20–25 range is 27 ± 4%, and is consistent with the observed value obtained for AGNs located within 20 Mpc.
galaxies, active, Seyfert, quasars, general, X-rays, diffuse background
2041-8205
Ricci, C.
82c8f75d-8215-4054-8b69-4cd30ab2d774
Ueda, Y.
03f584c1-9f26-484f-91a3-cf69654b933e
Koss, M.J.
c915109e-45f4-4d05-8bcd-7849d979f68e
Trakhtenbrot, B.
1bbbe48f-d3b9-4bf0-a509-7d006a17bbc7
Bauer, F.E.
4090334d-93b3-4fd4-83bf-3c65385dce47
Gandhi, P.
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9
Ricci, C.
82c8f75d-8215-4054-8b69-4cd30ab2d774
Ueda, Y.
03f584c1-9f26-484f-91a3-cf69654b933e
Koss, M.J.
c915109e-45f4-4d05-8bcd-7849d979f68e
Trakhtenbrot, B.
1bbbe48f-d3b9-4bf0-a509-7d006a17bbc7
Bauer, F.E.
4090334d-93b3-4fd4-83bf-3c65385dce47
Gandhi, P.
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9

Ricci, C., Ueda, Y., Koss, M.J., Trakhtenbrot, B., Bauer, F.E. and Gandhi, P. (2015) Compton-thick accretion in the local universe. The Astrophysical Journal Letters, 815 (1), [L13]. (doi:10.1088/2041-8205/815/1/L13).

Record type: Article

Abstract

Heavily obscured accretion is believed to represent an important stage in the growth of supermassive black holes and to play an important role in shaping the observed spectrum of the cosmic X-ray background. Hard X-ray (E > 10 keV) selected samples are less affected by absorption than samples selected at lower energies, and are therefore one of the best ways to detect and identify Compton-thick (CT, log NH ≥ 24) active galactic nuclei (AGNs). In this letter we present the first results of the largest broadband (0.3–150 keV) X-ray spectral study of hard X-ray selected AGNs to date, focusing on the properties of heavily obscured sources. Our sample includes the 834 AGNs (728 non-blazar, average redshift z sime 0.055) reported in the 70-month catalog of the all-sky hard X-ray Swift/Burst Alert Monitor survey. We find 55 CT AGNs, which represent 7.6-2.1+1.1 % of our non-blazar sample. Of these, 26 are reported as candidate CT AGNs for the first time. We correct for selection bias and derive the intrinsic column density distribution of AGNs in the local universe in two different luminosity ranges. We find a significant decrease in the fraction of obscured Compton-thin AGNs for increasing luminosity, from 46 ± 3% (for log L14-195 = 40–43.7) to 39 ± 3% (for log L14-195 = 43.7–46). A similar trend is also found for CT AGNs. The intrinsic fraction of CT AGNs with log NH = 24–25 normalized to unity in the NH = 20–25 range is 27 ± 4%, and is consistent with the observed value obtained for AGNs located within 20 Mpc.

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Accepted/In Press date: 13 November 2015
e-pub ahead of print date: 9 December 2015
Published date: 10 December 2015
Keywords: galaxies, active, Seyfert, quasars, general, X-rays, diffuse background
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 400033
URI: http://eprints.soton.ac.uk/id/eprint/400033
ISSN: 2041-8205
PURE UUID: 1282bb3d-1898-46e4-a3c3-b9e0e804d11b
ORCID for P. Gandhi: ORCID iD orcid.org/0000-0003-3105-2615

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Date deposited: 07 Sep 2016 09:38
Last modified: 24 Apr 2020 00:36

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