A precise deuterium abundance: Re-measurement of the z=3.572 absorption
  system towards the quasar PKS1937-101
  The primordial deuterium abundance probes fundamental physics during the Big
Bang Nucleosynthesis and can be used to infer cosmological parameters.
Observationally, the abundance can be measured using absorbing clouds along the
lines of sight to distant quasars. Observations of the quasar PKS1937--101
contain two absorbers for which the deuterium abundance has previously been
determined. Here we focus on the higher redshift one at $z_{abs} = 3.572$. We
present new observations with significantly increased signal-to-noise ratio
which enable a far more precise and robust measurement of the deuterium to
hydrogen column density ratio, resulting in D/H = $2.62\pm0.05\times10^{-5}$.
This particular measurement is of interest because it is among the most precise
assessments to date and it has been derived from the second lowest
column-density absorber [N(HI) $=17.9\mathrm{cm}^{-2}$] that has so-far been
utilised for deuterium abundance measurements. The majority of existing
high-precision measurements were obtained from considerably higher column
density systems [i.e. N(HI) $>19.4\mathrm{cm}^{-2}$]. This bodes well for
future observations as low column density systems are more common.
