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  1. OA@INAF
  2. PRODOTTI RICERCA INAF
  3. 1 CONTRIBUTI IN RIVISTE (Journal articles)
  4. 1.01 Articoli in rivista
Please use this identifier to cite or link to this item: http://hdl.handle.net/20.500.12386/29077
Title: The Chandra COSMOS Legacy Survey: Compton thick AGN at high redshift
Authors: LANZUISI, Giorgio 
Civano, F.
MARCHESI, STEFANO 
COMASTRI, Andrea 
Brusa, M.
GILLI, Roberto 
Vignali, C.
Zamorani, G.
Brightman, M.
Griffiths, R. E.
Koekemoer, A. M.
Issue Date: 2018
Journal: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 
Number: 480
Issue: 2
First Page: 2578
Abstract: The existence of a large population of Compton thick (CT; N<SUB>H</SUB> > 10<SUP>24</SUP> cm<SUP>-2</SUP>) 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 N<SUB>H</SUB> > 10<SUP>24</SUP> cm<SUP>-2</SUP> 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 (f<SUB>CT</SUB>) from ∼0.30 to ∼0.55 from low to high redshift. When rescaled to a common luminosity (log(L<SUB>X</SUB>/ erg s<SUP>-1</SUP>) = 44.5), we find an increase from f<SUB>CT</SUB> = 0.19_{-0.06}^{+0.07} to 0.30_{-0.08}^{+0.10} and f<SUB>CT</SUB> = 0.49_{-0.11}^{+0.12} from low to high z. This evolution can be parametrized as f<SUB>CT</SUB> = 0.11_{-0.04}^{+0.05}(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.
URI: http://hdl.handle.net/20.500.12386/29077
URL: https://www.aanda.org/articles/aa/full_html/2019/01/aa32383-17/aa32383-17.html
ISSN: 0035-8711
DOI: 10.1093/mnras/sty2025
Bibcode ADS: 2018MNRAS.480.2578L
Fulltext: open
Appears in Collections:1.01 Articoli in rivista

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