Physics
Scientific paper
Mar 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999adspr..23.1155g&link_type=abstract
Advances in Space Research, Vol. 23, No. 5 - 6, p. 1155 - 1160
Physics
3
Quasars: X-Ray Background, Quasars: X-Ray Absorption
Scientific paper
The question of whether there exists a large population of dust obscured QSOs is currently very controversial. In favour of this hypothesis are models for the origin of the X-ray background (XRB) and also the unified model of AGN which both invoke large populations of obscured QSOs. For example, Madau et al. (1994) suggest a population of QSOs with NH≡1024cm-2 or AV= 1000m to improve the fit to the XRB between 1 < E < 100 keV. Arguments contradicting this theory include those of Boyle and di Matteo (1995) who claim that the tight X-ray/optical flux ratio relation for QSOs precludes the existence of a large population of objects obscured by significant amounts of intrinsic dust. Here, the authors follow Madau et al. (1994) and Comastri et al. (1995) to make fits to the XRB using obscured QSO populations and investigate whether selection effects may allow a tight distribution of X-ray/optical ratios to be maintained. It is found that even for a flat distribution of absorbing columns, reasonable fits to the XRB can be obtained while both optical and X-ray absorption combine to produce the tight observed X-ray/optical correlation.
Gunn Katherine F.
Shanks Tom
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