# A precise deuterium abundance: Re-measurement of the z=3.572 absorption system towards the quasar PKS1937-101

## TL;DR

This paper presents a highly precise measurement of the primordial deuterium abundance from a low column-density absorber at redshift 3.572, improving the accuracy of cosmological parameters derived from Big Bang Nucleosynthesis.

## Contribution

The study provides the most precise deuterium abundance measurement from a low column-density system, demonstrating the viability of using such systems for future cosmological studies.

## Key findings

- Deuterium to hydrogen ratio D/H = (2.62 ± 0.05) x 10^{-5}
- Achieved higher precision with increased signal-to-noise ratio
- Low column-density systems are promising for future deuterium measurements

## Abstract

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.