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# Effect of a partial coverage of quasar broad-line regions by intervening H$$_2$$-bearing clouds

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### Abstract

We consider the effect of a partial coverage of quasar broad-line regions (QSO BLRs) by intervening H$$_2$$-bearing clouds when a part of quasar (QSO) radiation passes by a cloud not taking part in formation of an absorption-line system in the QSO spectrum. That leads to modification of observable absorption line profiles and consequently to a bias in physical parameters derived from standard absorption line analysis. In application to the H$$_2$$ {absorption} systems the effect has been revealed in the analysis of H$$_2$$ absorption system in the spectrum of Q~1232+082 (Ivanchik et al. 2010, Balashev et al. 2011). We estimate a probability of the effect to be detected in QSO spectra. To do this we derive distribution of BLR sizes of high-z QSOs from Sloan Digital Sky Survey (SDSS) Data Release 9 (DR9) catalogue and assume different distributions of cloud sizes. We conclude that the low limit of the probability is about $$11\%$$. The latest researches shows that about a fifth of observed H$$_2$$ absorption systems can be partially covered. Accounting of the effect may allow to revise significantly physical parameters of interstellar clouds obtained by the spectral analysis.

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###### Journal
19 August 2015
1508.04750
10.1007/s10509-015-2459-4