Measurements of the deuterium abundance in quasar absorption systems
Abstract
Description
Observational constraints on the primordial deuterium-to-hydrogen ratio (D/H) can test theories of the early universe and provide constraints on models of big bang nucleosynthesis (BBN). We measure deuterium absorption in high-redshift, metal-poor QSO absorption systems and directly infer the value of primordial D/H. We present two measurements of D/H, and find D/H = 3.3 $\pm 0.3 \times 10^{-5}$ at $z=3.572$ towards QSO 1937-1009 and D/H = 4.0 $\pm 0.7 \times 10^{-5}$ at $z=2.504$ towards QSO 1009+2956. Both measurements use multiple-component Voigt profile analysis of high resolution, high signal-to-noise spectra and determinations of the Lyman continuum optical depth in low resolution spectra to constrain the column densities of deuterium and hydrogen. The measurements are consistent with a single primordial value of D/H = $3.4 \pm 0.3 \times 10^{-5}$. This is a relatively low value, which supports homogeneous models of BBN and standard models of galactic chemical evolution. With standard BBN, we find a cosmological baryon-to-photon ratio, $η= 5.1 \pm 0.3 \times 10^{-10}$, and a present-day baryon density in units of the critical density, $Ω_b h_{100}^2 = 0.019 \pm 0.001$.
10 pages, 4 figures; to appear in the Proceedings of the Second Oak Ridge Symposium on Atomic & Nuclear Astrophysics, (Oak Ridge, TN, December 2-6, 1997), ed. A. Mezzacappa (Institute of Physics, Bristol)
10 pages, 4 figures; to appear in the Proceedings of the Second Oak Ridge Symposium on Atomic & Nuclear Astrophysics, (Oak Ridge, TN, December 2-6, 1997), ed. A. Mezzacappa (Institute of Physics, Bristol)