Advanced

High-redshift AGN in the Chandra Deep Fields : The obscured fraction and space density of the sub-L* population

Vito, F.; Brandt, W. N.; Yang, G.; Gilli, R.; Luo, B.; Vignali, C.; Xue, Y. Q.; Comastri, A.; Koekemoer, A. M. and Lehmer, B. D., et al. (2018) In Monthly Notices of the Royal Astronomical Society 473(2). p.2378-2406
Abstract

We investigate the population of high-redshift (3≤z < 6) active galactic nuclei (AGN) selected in the two deepest X-ray surveys, the 7 Ms Chandra Deep Field-South and 2 Ms Chandra Deep Field-North. Their outstanding sensitivity and spectral characterization of faint sources allow us to focus on the sub-L* regime (logLX ≲ 44), poorly sampled by previous works using shallower data, and the obscured population. Taking fully into account the individual photometric-redshift probability distribution functions, the final sample consists of ≈102 X-ray-selected AGN at 3 ≤ z < 6. The fraction of AGN obscured by column densities logNH > 23 is ~0.6-0.8, once incompleteness effects are taken into account, with no... (More)

We investigate the population of high-redshift (3≤z < 6) active galactic nuclei (AGN) selected in the two deepest X-ray surveys, the 7 Ms Chandra Deep Field-South and 2 Ms Chandra Deep Field-North. Their outstanding sensitivity and spectral characterization of faint sources allow us to focus on the sub-L* regime (logLX ≲ 44), poorly sampled by previous works using shallower data, and the obscured population. Taking fully into account the individual photometric-redshift probability distribution functions, the final sample consists of ≈102 X-ray-selected AGN at 3 ≤ z < 6. The fraction of AGN obscured by column densities logNH > 23 is ~0.6-0.8, once incompleteness effects are taken into account, with no strong dependence on redshift or luminosity. We derived the high-redshift AGN number counts down to F0.5-2 keV = 7 × 10-18 erg cm-2 s-1, extending previous results to fainter fluxes, especially at z > 4. We put the tightest constraints to date on the low-luminosity end of AGN luminosity function at high redshift. The space density, in particular, declines at z > 3 at all luminosities, with only a marginally steeper slope for low-luminosity AGN. By comparing the evolution of the AGN and galaxy densities, we suggest that such a decline at high luminosities is mainly driven by the underlying galaxy population, while at low luminosities there are hints of an intrinsic evolution of the parameters driving nuclear activity. Also, the black hole accretion rate density and star formation rate density, which are usually found to evolve similarly at z ≲ 3, appear to diverge at higher redshifts.

(Less)
Please use this url to cite or link to this publication:
author
, et al. (More)
(Less)
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Galaxies: active, Galaxies: evolution, Galaxies: high-redshift, methods: data analysis, Surveys, X-rays: galaxies
in
Monthly Notices of the Royal Astronomical Society
volume
473
issue
2
pages
29 pages
publisher
OXFORD UNIV PRESS
external identifiers
  • scopus:85045939761
ISSN
0035-8711
DOI
10.1093/mnras/stx2486
language
English
LU publication?
yes
id
6fce7db2-8d81-4c87-b3d7-b5c1aa86f1f3
date added to LUP
2018-05-16 15:10:09
date last changed
2018-10-07 05:06:34
@article{6fce7db2-8d81-4c87-b3d7-b5c1aa86f1f3,
  abstract     = {<p>We investigate the population of high-redshift (3≤z &lt; 6) active galactic nuclei (AGN) selected in the two deepest X-ray surveys, the 7 Ms Chandra Deep Field-South and 2 Ms Chandra Deep Field-North. Their outstanding sensitivity and spectral characterization of faint sources allow us to focus on the sub-L<sub>*</sub> regime (logLX ≲ 44), poorly sampled by previous works using shallower data, and the obscured population. Taking fully into account the individual photometric-redshift probability distribution functions, the final sample consists of ≈102 X-ray-selected AGN at 3 ≤ z &lt; 6. The fraction of AGN obscured by column densities logN<sub>H</sub> &gt; 23 is ~0.6-0.8, once incompleteness effects are taken into account, with no strong dependence on redshift or luminosity. We derived the high-redshift AGN number counts down to F<sub>0.5-2 ke</sub>V = 7 × 10<sup>-18</sup> erg cm<sup>-2</sup> s<sup>-1</sup>, extending previous results to fainter fluxes, especially at z &gt; 4. We put the tightest constraints to date on the low-luminosity end of AGN luminosity function at high redshift. The space density, in particular, declines at z &gt; 3 at all luminosities, with only a marginally steeper slope for low-luminosity AGN. By comparing the evolution of the AGN and galaxy densities, we suggest that such a decline at high luminosities is mainly driven by the underlying galaxy population, while at low luminosities there are hints of an intrinsic evolution of the parameters driving nuclear activity. Also, the black hole accretion rate density and star formation rate density, which are usually found to evolve similarly at z ≲ 3, appear to diverge at higher redshifts.</p>},
  author       = {Vito, F. and Brandt, W. N. and Yang, G. and Gilli, R. and Luo, B. and Vignali, C. and Xue, Y. Q. and Comastri, A. and Koekemoer, A. M. and Lehmer, B. D. and Liu, T. and Paolillo, M. and Ranalli, P. and Schneider, D. P. and Shemmer, O. and Volonteri, M. and Wang, J.},
  issn         = {0035-8711},
  keyword      = {Galaxies: active,Galaxies: evolution,Galaxies: high-redshift,methods: data analysis,Surveys,X-rays: galaxies},
  language     = {eng},
  month        = {01},
  number       = {2},
  pages        = {2378--2406},
  publisher    = {OXFORD UNIV PRESS},
  series       = {Monthly Notices of the Royal Astronomical Society},
  title        = {High-redshift AGN in the Chandra Deep Fields : The obscured fraction and space density of the sub-L<sub>*</sub> population},
  url          = {http://dx.doi.org/10.1093/mnras/stx2486},
  volume       = {473},
  year         = {2018},
}