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 logNHI=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 logNDI=16.19+/-0.04 cm-2, best constrained by the deuterium Ly11 line. We measure logD/H=-4.48+/-0.06, which when combined with previous measurements along QSO sight lines gives a best estimate of logD/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 Ωbh2=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 NHI. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.