A Caltech Library Service

The Chandra COSMOS Legacy Survey: Compton thick AGN at high redshift

Lanzuisi, G. and Civano, F. and Marchesi, S. and Comastri, A. and Brusa, M. and Gilli, R. and Vignali, C. and Zamorani, G. and Brightman, M. and Griffiths, R. E. and Koekemoer, A. M. (2018) The Chandra COSMOS Legacy Survey: Compton thick AGN at high redshift. Monthly Notices of the Royal Astronomical Society, 480 (2). pp. 2578-2592. ISSN 0035-8711. doi:10.1093/mnras/sty2025.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Accepted Version
See Usage Policy.

[img] PDF - Supplemental Material
See Usage Policy.


Use this Persistent URL to link to this item:


The existence of a large population of Compton thick (CT; N_H > 10^(24) cm^(−2)) active galactic nuclei (AGN) is a key ingredient of most cosmic X-ray background synthesis models. However, direct identification of these sources, especially at high redshift, is difficult due to flux suppression and complex spectral shape produced by CT obscuration. We explored the Chandra Cosmological Evolution Survey (COSMOS) Legacy point source catalogue, comprising 1855 sources to select, via X-ray spectroscopy, a large sample of CT candidates at high redshift. Adopting a physical model to reproduce the toroidal absorber and a Monte-Carlo sampling method, we selected 67 individual sources with >5 per cent probability of being CT, in the redshift range 0.04 ≲ z ≲ 3.5. The sum of the probabilities above NH > 10^(24) cm^(−2) gives a total of 41.9 effective CT, corrected for classification bias. We derive number counts in the 2–10 keV band in three redshift bins. The observed log N–log S is consistent with an increase of the intrinsic CT fraction (fCT) from ∼0.30 to ∼0.55 from low to high redshift. When rescaled to a common luminosity (log(L_X/ erg s^(−1)) = 44.5), we find an increase from f_(CT) = 0.19^(+0.07)_(−0.06) to 0.30^(+0.10)_(−0.08) and f_(CT) = 0.49^(+0.12)_(−0.11) from low to high z⁠. This evolution can be parametrized as f_(CT) = 0.11^(+0.05)_(−0.04) (1+z)^(1.11±0.13)⁠. Thanks to Hubble Space Telescope-Advanced Camera for Surveys deep imaging, we find that the fraction of CT AGN in mergers/interacting systems increases with luminosity and redshift and is significantly higher than for non-CT AGN hosts.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Lanzuisi, G.0000-0001-9094-0984
Civano, F.0000-0002-2115-1137
Marchesi, S.0000-0001-5544-0749
Comastri, A.0000-0003-3451-9970
Brusa, M.0000-0002-5059-6848
Vignali, C.0000-0002-8853-9611
Brightman, M.0000-0002-8147-2602
Koekemoer, A. M.0000-0002-6610-2048
Additional Information:© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2018 July 25. Received 2018 July 25; in original form 2018 March 22. The authors thank the referee for the constructive comments and recommendations that helped to improve the readability and quality of the paper. This research has made use of data obtained from the Chandra Data Archive and software provided by the Chandra X-ray Center (CXC) in the CIAO application package. The authors acknowledge financial support from the CIG grant ‘eEASY’ no. 321913, from ASI-INAF grant no. 2014-045-R.0, and from PRIN-INAF-2014 (‘Windy Black Holes Combing Galaxy Evolution’).
Funding AgencyGrant Number
European Research Council (ERC)321913 eEasy
Agenzia Spaziale Italiana (ASI)2014-045-R.0
Istituto Nazionale di Astrofisica (INAF)PRIN-INAF-2014
Subject Keywords:galaxies: active, galaxies: nuclei, X-rays: galaxies
Issue or Number:2
Record Number:CaltechAUTHORS:20181205-163501777
Persistent URL:
Official Citation:G Lanzuisi, F Civano, S Marchesi, A Comastri, M Brusa, R Gilli, C Vignali, G Zamorani, M Brightman, R E Griffiths, A M Koekemoer; The Chandra COSMOS Legacy Survey: Compton thick AGN at high redshift, Monthly Notices of the Royal Astronomical Society, Volume 480, Issue 2, 21 October 2018, Pages 2578–2592,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91528
Deposited By: George Porter
Deposited On:06 Dec 2018 15:31
Last Modified:16 Nov 2021 03:42

Repository Staff Only: item control page