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Title:
The Quest for Obscured AGN at Cosmological Distances: Infrared Power-Law Galaxies
Authors:
Alonso-Herrero, A.; Donley, J. L.; Rieke, G. H.; Rigby, J. R.; Pérez-González, P. G.
Publication:
Highlights of Spanish Astrophysics IV, Proceedings of the seventh Scientific Meeting of the Spanish Astronomical Society (SEA) held in Barcelona, Spain, September 12-15, 2006. Edited by F. Figueras, Departament d'Astronomia i Meteorologia, Universitat de Barcelona-IEEC; J.M. Girart,Institute de Ciències de l'Espai, CSIC-IEEC; M. Hernanz, Institute de Ciències de l'Espai, CSIC-IEEC; C. Jordi, Departament d'Astronomia i Meteorologia, Universitat de Barcelona-IEEC. ISBN: 978-1-4020-6000-7 (ebook). Published by Springer, Dordrecht, 2007, p.143
Publication Date:
00/2007
Origin:
ADS
Bibliographic Code:
2007hsa..conf..143A

Abstract

We summarize multiwavelength properties of a sample of galaxies in the CDF-N and CDF-S whose Spectral Energy Distributions (SEDs) exhibit the characteristic power-law behavior expected for AGN in the Spitzer/IRAC 3.6-8micron bands. AGN selected this way tend to comprise the majority of high X-ray luminosity AGN, whereas AGN selected via other IRAC color-color criteria might contain more star-formation dominated galaxies. Approximately half of these IR power-law galaxies in the CDF-S are detected in deep (1Ms) Chandra X-ray imaging, although in the CDF-N (2Ms) about 77% are detected at the 3sigma level. The SEDs and X-ray upper limits of the sources not detected in X-rays are consistent with those of obscured AGN, and are significantly different from those of massive star-forming galaxies. About 40% of IR power-law galaxies detected in X-rays have SEDs resembling that of an optical QSO and morphologies dominated by bright point source emission. The remaining 60% have SEDs whose UV and optical continuum are much steeper (obscured) and more extended morphologies than those detected in X-rays. Most of the IR power-law galaxies not detected in X-rays have IR (8-1000micron above 10^12Lsun, and X-ray (upper limits) to mid-IR ratios similar to those of local warm (ie, hosting an AGN) ULIRGs. The SED shapes of power-law galaxies are consistent with the obscured fraction (4:1) as derived from the X-ray column densities, if we assume that all the sources not detected in X-rays are heavily absorbed. IR power-law galaxies may account for between 20% and 50% of the predicted number density of mid-IR detected obscured AGN. The remaining obscured AGN probably have rest-frame SEDs dominated by stellar emission.
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