期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 358, 期 2, 页码 693-704出版社
OXFORD UNIV PRESS
DOI: 10.1111/j.1365-2966.2005.08821.x
关键词
surveys; galaxies : active; X-rays : diffuse background; X-ray : galaxies; X-rays : general
We present the results of a detailed spectral analysis of optically faint hard X-ray sources in the Chandra deep fields selected on the basis of their high X-ray to optical flux ratio (X/O). The stacked spectra of high X/O sources in both Chandra deep fields, fitted with a single power-law model, are much harder than the spectrum of the X-ray background (XRB). The average slope is also insensitive to the 2-8 keV flux, being approximately constant around Gamma similar or equal to 1 over more than two decades, strongly indicating that high X/O sources represent the most obscured component of the XRB. For about half of the sample, a redshift estimate (in most of the cases a photometric redshift) is available from the literature. Individual fits of a few of the brightest objects and of stacked spectra in different redshift bins imply column densities in the range 10(22)-10(23.5) cm(-2). A trend of increasing absorption towards higher redshifts is suggested.
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