Multi-phase gas properties of extremely strong intervening DLAs towards
  quasars
  We present the results of a spectroscopic analysis of extremely strong damped
Lyman-{\alpha} absorbers (ESDLAs, log N(Hi)>=21.7) observed with VLT-XShooter.
ESDLAs probe gas from within the star-forming disk of the associated galaxies
and thus ESDLAs provide a unique opportunity to study the interstellar medium
of galaxies at high-redshift. We report column densities (N), equivalent widths
(w), and the kinematic spread ({\Delta} v90) of species from neutral, singly
ionised, and higher ionisation species. We find that, using the dust correction
prescription, the measured metallicities are consistent for singly ionised gas
species such as Pii, S ii, Si ii, Mnii and Crii, and Znii in all ESDLAs within
3-sigma uncertainty. We find that the distributions of N(Ari)/N(Hi) ratio in
DLAs and ESDLAs are similar. We further report that ESDLAs do not show a strong
deficiency of Ari relative to other {\alpha}-capture elements as is seen in
DLAs. This supports the idea that the mentioned under-abundance of Ari in DLAs
is possibly caused by the presence of background UV photons that penetrate the
low N(Hi) clouds to ionise Ari, but they cannot penetrate deep enough in the
high N(Hi) ESDLA environment. The w(Mgii lambda2796) distribution in ESDLAs is
found to be similar to that of metal-rich Ci-selected absorbers, but the
velocity spread of their Mgii profile is different. For higher ionisation
species (such as C iv and Si iv), {\Delta} v90 is similar in the two
populations, while the {\Delta} v90 of singly ionised species is smaller for
ESDLAs. This suggests that the ESDLAs sample a different Hi region of their
associated galaxy compared to the general DLA population. We further study the
N(Cl i) distribution in high-redshift DLA and ESDLA sightlines, as Cl i is a
good tracer of H2 gas. The N(Cl i)-N(H2) correlation is followed by all the
clouds (ESDLAs and otherwise) having log N(H2)<22.
