Partial coverage of the Broad Line Region of Q1232+082 by an intervening
  H2-bearing cloud
  We present a detailed analysis of the partial coverage of the Q1232+082 (z_em
=2.57) broad line region 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 QSO intrinsic continuum
source completely but only part of the Broad Line Region (BLR). We find that
only 48\pm6 % of the C IV BLR emission is covered by the C I absorbing gas. We
observe residual light (~6 %) as well in the bottom of the O I {\lambda}1302
absorption from the cloud, redshifted on top of the QSO Lyman-{\alpha} 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:
n_H2~110 cm^{-3} for the H_2-bearing core and n_H ~30 cm^{-3} for the neutral
envelope. Given the column densities, N(H2)=(3.71\pm0.97)\times10^19 cm^{-2}
and N(H I)=(7.94\pm1.6)\times10^20 cm^{-2}, we derive the linear size of the
H_2-bearing core and the neutral envelope along the line of sight to be
l_H2~0.15^{+0.05}_{-0.05} pc and l_HI~8.2^{+6.5}_{-4.1} pc, respectively. We
estimate the size of the C IV 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 ~0.18 pc, 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-{\alpha} emission means that the Lyman-{\alpha} BLR is probably
fully covered but that the Lyman-{\alpha} emission extends well beyond the
limits of the BLR.
