Abstract

We present a detailed analysis of the partial coverage of the Q1232+082 (z em= 2.57) broad-line region (BLR) by an intervening H 2-bearing cloud at z abs= 2.3377. Using curve of growth analysis and line profile fitting, we demonstrate that the H 2-bearing component of the cloud covers the quasi-stellar object (QSO) intrinsic continuum source completely but only part of the BLR. We find that only 48 ± 6 per cent of the Civ BLR emission is covered by the Ci absorbing gas. We observe residual light (?6 per cent) as well in the bottom of the Oi?1302 absorption from the cloud, redshifted on top of the QSO Lyman ? emission line. Therefore, the extent of the neutral phase of the absorbing cloud is not large enough to cover all of the background source. The most likely explanation for this partial coverage is the small size of the intervening cloud, which is comparable to the BLR size. We estimate the number densities in the cloud: ? 110cm -3 for the H 2-bearing core and n H? 30cm -3 for the neutral envelope. Given the column densities, N(H 2) = 3.71 ± 0.97 × 10 19cm -2 and N(Hi) = 7.94 ± 1.6 × 10 20cm -2, we derive the linear size of the H 2-bearing core and the neutral envelope along the line of sight to be ? 0.15 +0.05 -0.05pc and ? 8.2 +6.5 -4.1pc, respectively. We estimate the size of the Civ BLR by two ways: (i) extrapolating size-luminosity relations derived from reverberation observations and (ii) assuming that the H 2-bearing core and the BLR are spherical in shape and the results are ?0.26 and ?0.18pc, respectively. The large size we derive for the extent of the neutral phase of the absorbing cloud together with a covering factor of ?0.94 of the Lyman ? emission means that the Lyman ? BLR is probably fully covered but that the Lyman ? emission extends well beyond the limits of the BLR. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.