Partial coverage means that only part of the background source is covered by the absorbing cloud. Mainly this can be a consequence of the absorbing cloud size being comparable or even smaller than the projected extent of the background source. This effect is rare for intervening systems, when a distance between a cloud and quasar is large. To date, the partial coverage has been found only in two cases - for H₂ absorption clouds in spectra Q 1232+082 and Q 0528-250. Analysis of the partial coverage of Q 1232+082 allowed to estimate the size of Broad Line Region (CIV) and mass of the central black-hole, associated with Q 1232+082. Tacking into account the partial coverage effect for H₂ cloud in the spectrum of Q 0528-250 allows us to get a consistent fit of H₂ absorption system, that has not been done before. In this work we have checked all other molecular absorption systems in quasar spectra (25) and have found that partial coverage of emission regions of QSOs by intervening clouds is not rare and is crucial in any analyses of H₂ bearing systems, when studying the physical state of high redshift interstellar medium.

Page created on April 18, 2014.