High Deuterium Abundance in a New Quasar Absorber

Abstract

We present a new analysis of an absorption system in the spectrum of Q0014+813, with particular attention to a single cold cloud at redshift $z=2.797957$. Features are identified at this redshift corresponding to SiIII, SiIV, CIV, DI, and HI, all consistent with purely thermal broadening at $T\approx 19,000$K. The deuterium identification is confirmed by its narrow width and precise agreement with the silicon and carbon redshifts. The HI column is well constrained by a slightly damped profile in the blue wing of Ly$\alpha$, and the DI column by its saturation, leading to a 95\% confidence lower limit $(D/H)>0.7\times 10^{-4}$. The abundance is measured from line fits to be $(D/H)=1.9_{-0.9}^{+1.6}\times 10^{-4}$ , in agreement with the high deuterium abundance previously found in the $z=3.32$ system in the same quasar spectrum. This system strengthens the case for a high universal primordial deuterium abundance and low cosmic baryon density ($\eta =1.7\times 10^{-10}$, ${\Omega }_b{h}^2=0.006$), for which Standard Big Bang Nucleosynthesis gives concordant predictions for helium-4 and lithium-7 abundances. Implications for Galactic chemical evolution and the baryonic and nonbaryonic dark matter problems are briefly discussed.

25 pages, gzipped postscript file, submitted to Astron. J