Measurements of the deuterium abundance in quasar absorption systems

TL;DR

This paper measures the primordial deuterium abundance in high-redshift quasar absorption systems to test big bang nucleosynthesis models and determine cosmological baryon density.

Contribution

It provides two new high-precision measurements of D/H in quasar systems, supporting a consistent primordial value and standard cosmological models.

Findings

Primordial D/H = (3.4 ± 0.3) × 10^{-5}

Supports homogeneous BBN models

Determines baryon density Ω_b h^2 = 0.019 ± 0.001

Abstract

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, $\eta = 5.1 \pm 0.3 \times 10^{-10}$, and a present-day baryon density in units of the critical density, $\Omega_b h_{100}^2 = 0.019 \pm 0.001$.