|University of California – San Diego
|Physics; Astrophysics; Big Bang Nucleosynthesis; Deuterium; Lyman-Alpha Forest; Observational Cosmology; Quasars
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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=1017.41cmm) which exhibits very low metal content indicating pristine conditions ([Si/H]=-3.3 ± 0.8). This value, 105D/H=2.50± 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=1020.8 cmm) and measure D/H to be 2.359 ± 0.095 emdash 2σ 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.