X-ray spectral analysis of optically faint sources in the Chandra deep fields |
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| Authors: | Francesca Civano rea Comastri Marcella Brusa |
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| Institution: | Dipartimento di Astronomia, Universitàdi Bologna, via Ranzani 1, I-40127 Bologna, Italy;INAF –Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna, Italy;Max Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching, Germany |
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| Abstract: | 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 Γ? 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 1022–1023.5 cm?2 . A trend of increasing absorption towards higher redshifts is suggested. |
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| Keywords: | surveys galaxies: active X-rays: diffuse background X-ray: galaxies X-rays: general |
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