Chemical enrichment and host galaxies of extremely-strong intervening
  DLAs towards quasars
  We present the results from VLT/X-shooter spectroscopic observations of 11
extremely strong intervening damped Lyman-alpha absorbers (ESDLAs) initially
selected as high N(Hi) (i.e.>=5x10^21 cm-2) candidates from the Sloan Digital
Sky Survey (SDSS). We confirm the high Hi column densities which we measure to
be in the range log N(Hi) = 21.6-22.4. Molecular hydrogen is detected with high
column densities (N(H_2)>=10^18 cm-2) in five out of eleven systems, three of
which are reported here for the first time. We compare the chemical properties
of this sample of ESDLAs, supplemented with literature measurements, to that of
DLAs located at the redshift of long-duration gamma-ray bursts (GRB-DLAs). We
confirm that the two populations are almost indistinguishable in terms of
chemical enrichment, H_2 column density and gas kinematics. All this suggests
that ESDLAs and GRB-DLAs probe similar galactic environments. We search for the
galaxy counterparts of ESDLAs and find associated emission lines in three out
of eleven systems, two of which are reported here for the first time (towards
the quasars SDSS J002503.03+114547.80 and SDSS J114347.21+142021.60,
respectively). The measured separations between the quasar sightlines and the
emission associated with the ESDLA galaxy are all very small (rho < 3 kpc).
While the small impact parameters are similar to what is observed for GRB-DLAs,
the associated star-formation rates are on average lower than seen for GRB host
galaxies. This is explained by long-duration GRBs being associated with the
death of massive stars, hence pinpointing regions of active star formation in
the GRB host galaxies. Our observations support the suggestion from the
literature that ESDLAs could act as blind analogues of GRB-DLAs, probing high
column density neutral gas in the heart of high-redshift galaxies, without any
prior on the instantaneous star-formation rate.
