Down-the-barrel observations of a multiphase quasar outflow at high
  redshift: VLT/X-shooter spectroscopy of the proximate molecular absorber at
  z=2.631 towards SDSS J001514+184212
  We present UV to NIR spectroscopic observations of the quasar J0015+1842 and
its proximate molecular absorber at z=2.631. The [OIII] emission line of the
quasar is composed of a broad (FWHM~1600 km/s), spatially-unresolved component,
blueshifted by ~600 km/s from a narrow, spatially-resolved component (FWHM~650
km/s). The wide, blueshifted, unresolved component is consistent with the
presence of outflowing gas in the nuclear region. The narrow component can be
further decomposed into a blue and a red blob with velocity width of several
hundred km/s each, seen ~5 pkpc on opposite spatial locations from the nuclear
emission, indicating outflows over galactic scales. The presence of ionised gas
over kpc-scales is also seen from a weak CIV emission component, detected in
the trough of a saturated CIV absorption that removes the strong nuclear
emission from the quasar.
  Towards the nuclear emission, we observe absorption lines from atomic species
in various ionisation and excitation stages and confirm the presence of strong
H2 lines. The overall absorption profile is very wide, spread over ~600 km/s,
roughly matching in velocities the blue narrow [OIII] blob. From detailed
investigation of the chemical and physical conditions in the absorbing gas, we
infer densities of about nH ~ 10^4-10^5 cm^-3 in the cold (T~100 K) H2-bearing
gas, which we find to be located at ~10 kpc distances from the central UV
source.
  We conjecture that we are witnessing different manifestations of a same
AGN-driven multi-phase outflow, where approaching gas is intercepted by the
line of sight to the nucleus. We corroborate this picture by modelling the
scattering of Ly-a photons from the central source through the outflowing gas,
reproducing the peculiar Ly-a absorption-emission profile, with a damped Ly-a
absorption in which red-peaked, spatially offset and extended Ly-a emission is
seen. [abridged]
