A quasar reddened by a sub-parsec sized, metal-rich and dusty cloud in a
  damped Lyman-alpha absorber at z=2.13
  We present a detailed analysis of a red quasar at z=2.32 with an intervening
damped Lyman-alpha absorber (DLA) at z=2.13. Using high quality data from the
X-shooter spectrograph at ESO Very Large Telescope we find that the absorber
has a metallicity consistent with Solar. We observe strong C I and H$_2$
absorption indicating a cold, dense absorbing medium. Partial coverage effects
are observed in the C I lines, from which we infer a covering fraction of $27
\pm 6$ % and a physical diameter of the cloud of 0.1 pc. From the covering
fraction and size, we estimate the size of the background quasar's broad line
region. We search for emission from the DLA counterpart in optical and
near-infrared imaging. No emission is observed in the optical data. However, we
see tentative evidence for a counterpart in the H and K' band images. The DLA
shows high depletion (as probed by [Fe/Zn]=-1.22) indicating that significant
amounts of dust must be present in the DLA. By fitting the spectrum with
various dust reddened quasar templates we find a best-fitting amount of dust in
the DLA of $A(V)_{\rm DLA}=0.28 \pm 0.01|_{\rm stat} \pm 0.07|_{\rm sys}$. We
conclude that dust in the DLA is causing the colours of this intrinsically very
luminous background quasar to appear much redder than average quasars, thereby
not fulfilling the criteria for quasar identification in the Sloan Digital Sky
Survey. Such chemically enriched and dusty absorbers are thus underrepresented
in current samples of DLAs.
