Constraints on the relative sizes of intervening Mg II-absorbing clouds and quasar emitting regions

In this paper, the authors investigate whether the differing beam sizes of the continuum source and broad-line region of Sloan Digital Sky Survey (SDSS) quasars produce a discrepancy between the incidence of strong MgII absorbers illuminated by the quasar continuum region and those of absorbers illuminated by both continuum and broad-line region light. The authors performed a semi-automated search for strong Mg II absorbers in the SDSS Data Release 7 quasar sample. The authors see no difference in the sight-line number density of strong MgII absorbers superimposed on quasar broad emission lines compared to those superimposed on continuum-dominated spectral regions. This suggests that the Mg II absorbing clouds typically observed as intervening absorbers in quasar spectra are larger than the beam sizes of both the continuum-emitting regions and broad line-emitting regions in the centers of quasars, corresponding to a lower limit of the order of 10 super( 17) cm for the characteristic size of an MgII absorbing cloud.