The Deuterium Abundance Towards Q1009+2956

Scott Burles; David Tytler

doi:10.1086/306341

paper

The Deuterium Abundance Towards Q1009+2956

arXiv:astro-ph/9712109 · doi:10.1086/306341

Abstract

We present a measurement of the deuterium to hydrogen ratio (D/H) in a metal-poor absorption system at redshift $z = 2.504$ towards the QSO 1009+2956. We apply the new method of Burles & Tytler (1997) to robustly determine D/H in high resolution \Lya forest spectra, and include a constraint on the neutral hydrogen column density determined from the Lyman continuum optical depth in low resolution spectra. We introduce six separate models to measure D/H and to assess the systematic dependence on the assumed underlying parameters. We find that the deuterium absorption feature contains a small amount of contamination from unrelated \ion{H}{1}. Including the effects of the contamination, we calculate the 67% confidence interval of D/H in this absorption system, log (D/H) $= - 4.4 0_{- 0.08}^{+ 0.06}$ . This measurement agrees with the low measurement by Burles & Tytler (1997) towards Q1937--1009, and the combined value gives the best determination of primordial D/H, log (D/H) $_{p} = - 4.4 7_{- 0.035}^{+ 0.030}$ or D/H $= 3.39 \pm 0.25 \times 1 0^{- 5}$ . Predictions from standard big bang nucleosynthesis (SBBN) give the cosmological baryon to photon ratio, $η = 5.1 \pm 0.3 \times 1 0^{- 10}$ , and the baryon density in units of the critical density, $Ω_{b} h^{2} = 0.019 \pm 0.001$ , where $H_{0} = 100 h$ \kms Mpc $^{- 1}$ . The measured value of (D/H) $_{p}$ implies that the primordial abundances of both $^{4}$ He and $^{7}$ Li are high, and consistent with some recent studies. Our two low measurements of primordial D/H also place strong constraints on inhomogeneous models of big bang nucleosynthesis.

47 pages, 24 figures, submitted to the Astrophysical Journal

The Deuterium Abundance Towards Q1009+2956

Abstract

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