UC San Diego

A precise determination of the light-element abundances produced during the epoch of Big Bang Nucleosynthesis (BBN) is an important probe of the early universe. The Deuterium-Hydrogen abundance ratio (D/H) is of particular importance due to its sensitivity to the cosmological baryon density, its use as a constraint of non-standard BBN scenarios and the fact that Deuterium is not created outside of BBN, but destroyed inside of stars at a predictable rate, so any Deuterium observed in interstellar or intergalactic gas is primordial. Due to the difficulty of measurements and relative rarity of appropriate conditions required to observe D in quasar absorption systems, there are only 15 published measurements of the primordial D/H in literature. Here we examine the primordial Deuterium-to-Hydrogen abundance ratio using high-resolution optical spectroscopy of diffuse gas towards two quasars. We measure \DI\ towards the bright Quasar J1201$+$0116 at moderate redshift ($z=2.98$) in a Lyman-Limit system (N=$10^{17.41}\cmm$) which exhibits very low metal content indicating pristine conditions ([Si/H]=$-3.3 \pm 0.8$). This value, $10^5$D/H=$2.50\pm 0.18$ is in complete agreement with D/H from the CMB and theory. We measure \DI\ in one component of DLA towards quasar J0744$+$2059 (N=$10^{20.8} \cmm$) and measure D/H to be $ 2.359 \pm 0.095$ \textemdash $2\sigma$\ lower than D/H from theory and the CMB. Additionally, we present measurements on the \lyaf\ towards 25 high-resolution QSO. The statistics we report are suitable for comparison to simulations, which are the primary means of extracting physical information from the Intergalactic Medium.