The Deuterium-to-Hydrogen Abundance Ratio toward the QSO SDSS J155810.16-003120.0

Abstract

We present a measurement of the D/H abundance ratio in a metal-poor damped Lyα (DLA) system along the sight line of QSO SDSS 1558-0031. The DLA system is at redshift z = 2.70262 and has a neutral column density of log N = 20.67 ± 0.05 cm -2 and a gas-phase metallicity [O/H] = -1.49, which indicates that deuterium astration is negligible. Deuterium absorption is observed in multiple Lyman series with a column density of log N = 16.19 ± 0.04 cm -2 , best constrained by the deuterium Ly11 line. We measure log D/H = -4.48 ± 0.06, which when combined with previous measurements along QSO sight lines gives a best estimate of log D/H = -4.55 ± 0.04, where the 1 σ error estimate comes from a jackknife analysis of the weighted means. Using the framework of standard big bang nucleosynthesis, this value of D/H translates into a baryon density of Ω b h 2 = 0.0213 ± 0.0013 ± 0.0004, where the error terms represent the 1 σ errors from D/H and the uncertainties in the nuclear reaction rates, respectively. Combining our new measurement with previous measurements of D/H, we no longer find compelling evidence for a trend of D/H with N .