A robust deuterium abundance; re-measurement of the z = 3.256 absorption system towards the quasar PKS 1937-101

The primordial deuterium abundance is an important tracer of the fundamental physics taking place during big bang nucleosynthesis. It can be determined from absorption features along the line of sight to distant quasars. The quasar PKS 1937-1009 contains two absorptions systems that have been used to measure the primordial deuterium abundance, the lower redshift one being at z_abs = 3.256. New observations of this absorber are of a substantially higher signal-to-noise ratio and thus permit a significantly more robust estimate of the primordial deuterium abundance, leading to a D I/H I ratio of 2.45 ± 0.28 × 10^-5. Whilst the precision of the new measurement presented here is below that obtained from the recent cosmological parameter measurements by the Planck Surveyor, our analysis illustrates how a statistical sample obtained using similarly high spectral signal-to-noise ratio can make deuterium a competitive and complementary cosmological parameter estimator and provide an explanation for the scatter seen between some existing deuterium measurements.