Professor David Alexander d.m.alexander@durham.ac.uk
Professor
Reliable identification of Compton-thick quasars at z~2 : Spitzer mid-infrared spectroscopy of HDF-oMD49
Alexander, D.M.; Chary, R.R.; Pope, A.; Bauer, F.E.; Brandt, W.N.; Daddi, E.; Dickinson, M.; Elbaz, D.; Reddy, N.A.
Authors
R.R. Chary
A. Pope
F.E. Bauer
W.N. Brandt
E. Daddi
M. Dickinson
D. Elbaz
N.A. Reddy
Abstract
Many models that seek to explain the origin of the unresolved X-ray background predict that Compton-thick active galactic nuclei (AGNs) are ubiquitous at high redshift. However, few distant Compton-thick AGNs have been reliably identified to date. Here we present Spitzer IRS spectroscopy and 3.6-70 μm photometry of a z=2.211 optically identified AGN (HDF-oMD49) that is formally undetected in the 2 Ms Chandra Deep Field-North (CDF-N) survey. The Spitzer IRS spectrum and spectral energy distribution of this object is AGN dominated, and a comparison of the energetics at X-ray wavelengths to those derived from mid-infrared (mid-IR) and optical spectroscopy shows that the AGN is intrinsically luminous (L2-10keV~3×1044 ergs s-1) but heavily absorbed by Compton-thick material (NH>>1024 cm-2) i.e., this object is a Compton-thick quasar. Adopting the same approach that we applied to HDF-oMD49, we found a further six objects at z~2-2.5 in the literature that are also X-ray weak/undetected but have evidence for AGN activity from optical and/or mid-IR spectroscopy, and show that all of these sources are likely to be Compton-thick quasars with L2-10keV>1044 ergs s-1. On the basis of the definition of Daddi et al., these Compton-thick quasars would be classified as mid-IR excess galaxies, and our study provides the first spectroscopic confirmation of Compton-thick AGN activity in a subsample of these z~2 mid-IR-bright galaxies. Using the four objects that lie in the CDF-N field, we estimate the space density of reliably identified Compton-thick quasars [Φ~(0.7-2.5)×10-5 Mpc-3 for L2-10keV>1044 ergs s-1 objects at z~2-2.5] and show that Compton-thick accretion was probably as ubiquitous as unobscured accretion in the distant universe.
Citation
Alexander, D., Chary, R., Pope, A., Bauer, F., Brandt, W., Daddi, E., …Reddy, N. (2008). Reliable identification of Compton-thick quasars at z~2 : Spitzer mid-infrared spectroscopy of HDF-oMD49. Astrophysical Journal, 687(2), 835-847. https://doi.org/10.1086/591928
Journal Article Type | Article |
---|---|
Publication Date | Jan 1, 2008 |
Deposit Date | Jan 30, 2012 |
Publicly Available Date | Mar 28, 2024 |
Journal | Astrophysical Journal |
Print ISSN | 0004-637X |
Electronic ISSN | 1538-4357 |
Publisher | American Astronomical Society |
Peer Reviewed | Peer Reviewed |
Volume | 687 |
Issue | 2 |
Pages | 835-847 |
DOI | https://doi.org/10.1086/591928 |
Keywords | Galaxies, Active galaxies, High-redshift, Infrared, Ultraviolet, X-rays. |
Files
Published Journal Article
(618 Kb)
PDF
Copyright Statement
© 2008. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
You might also like
A new discovery space opened by eROSITA: Ionised AGN outflows from X-ray selected samples
(2023)
Journal Article
DESI z ≳ 5 Quasar Survey. I. A First Sample of 400 New Quasars at z ∼ 4.7–6.6
(2023)
Journal Article
The Quasar Feedback Survey: characterizing CO excitation in quasar host galaxies
(2023)
Journal Article
Obscuration beyond the nucleus: infrared quasars can be buried in extreme compact starbursts
(2023)
Journal Article
Downloadable Citations
About Durham Research Online (DRO)
Administrator e-mail: dro.admin@durham.ac.uk
This application uses the following open-source libraries:
SheetJS Community Edition
Apache License Version 2.0 (http://www.apache.org/licenses/)
PDF.js
Apache License Version 2.0 (http://www.apache.org/licenses/)
Font Awesome
SIL OFL 1.1 (http://scripts.sil.org/OFL)
MIT License (http://opensource.org/licenses/mit-license.html)
CC BY 3.0 ( http://creativecommons.org/licenses/by/3.0/)
Powered by Worktribe © 2024
Advanced Search