HEAVILY OBSCURED ACTIVE GALACTIC NUCLEI IN HIGH-REDSHIFT LUMINOUS INFRARED GALAXIES

Journal Article · Wed Oct 20 04:00:00 EDT 2010 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/722/2/L238· OSTI ID:21452727

Treister, Ezequiel; Sanders, David B ^[1]; Urry, C Megan; Cardamone, Carolin N ^[2]; Schawinski, Kevin ^[3]

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1. Institute for Astronomy, 2680 Woodlawn Drive, University of Hawaii, Honolulu, HI 96822 (United States)
2. Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520 (United States)
3. Yale Center for Astronomy and Astrophysics, P.O. Box 208121, New Haven, CT 06520 (United States)

We take advantage of the rich multiwavelength data available in the Chandra Deep Field South (CDF-S), including the 4 Ms Chandra observations (the deepest X-ray data to date), in order to search for heavily obscured low-luminosity active galactic nuclei (AGNs) among infrared-luminous galaxies. In particular, we obtained a stacked rest-frame X-ray spectrum for samples of galaxies binned in terms of their IR luminosity or stellar mass. We detect a significant signal at E {approx} 1-8 keV, which we interpret as originating from a combination of emission associated with star formation processes at low energies combined with a heavily obscured AGN at E > 5 keV. We further find that the relative strength of this AGN signal decays with decreasing IR luminosity, indicating a higher AGN fraction for more luminous IR sources. Together, these results strongly suggest the presence of a large number of obscured AGNs in IR-luminous galaxies. Using samples binned in terms of stellar mass in the host galaxy, we find a significant excess at E = 6-7 keV for sources with M > 10{sup 11} M {sub sun}, consistent with a large obscured AGN population in high mass galaxies. In contrast, no strong evidence of AGN activity was found for less-massive galaxies. The integrated intensity at high energies indicates that a significant fraction of the total black hole growth, {approx}22%, occurs in heavily obscured systems that are not individually detected in even the deepest X-ray observations. There are also indications that the number of low-luminosity, heavily obscured AGNs does not evolve significantly with redshift, in contrast to the strong evolution seen in higher luminosity sources.

• OSTI ID: 21452727
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 722; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BLACK HOLES
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
EMISSION
EVOLUTION
GALACTIC EVOLUTION
GALAXIES
GALAXY NUCLEI
LUMINOSITY
MASS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RED SHIFT
SEYFERT GALAXIES
SIGNALS
SPECTRA
STAR EVOLUTION
STARS
X-RAY GALAXIES
X-RAY SPECTRA