Deuterium Abundance in the Most Metal-Poor Damped Lyman alpha System: Converging on Omega_baryons

TL;DR

This study measures the deuterium abundance in a very metal-poor DLA, refining the primordial deuterium value and constraining cosmological parameters like Omega_b h^2 and the spectral index n_s, thus contributing to our understanding of the early universe.

Contribution

It provides a new, precise measurement of the primordial deuterium abundance from the most metal-poor DLA, supporting convergence of this key cosmological parameter.

Findings

Deuterium abundance log(D/H) = -4.56 +/- 0.04 consistent with previous measurements.

Primordial deuterium abundance <log(D/H)_p> = -4.55 +/- 0.03.

Omega_b h^2 (BBN) = 0.0213 +/- 0.0010, supporting current cosmological models.

Abstract

The most metal-poor DLA known to date, at z = 2.61843 in the spectrum of the QSO Q0913+072, with an oxygen abundance only about 1/250 of the solar value, shows six well resolved D I Lyman series transitions in high quality echelle spectra recently obtained with the ESO VLT. We deduce a value of the deuterium abundance log (D/H) = -4.56+/-0.04 which is in good agreement with four out of the six most reliable previous determinations of this ratio in QSO absorbers. We find plausible reasons why in the other two cases the 1 sigma errors may have been underestimated by about a factor of two. The addition of this latest data point does not change significantly the mean value of the primordial abundance of deuterium, suggesting that we are now converging to a reliable measure of this quantity. We conclude that <log (D/H)_p> = -4.55+/-0.03 and Omega_b h^2 (BBN) = 0.0213+/-0.0010 (68% confidence limits). Including the latter as a prior in the analysis of the five year data of WMAP leads to a revised best-fitting value of the power-law index of primordial fluctuations n_s = 0.956+/-0.013 (1 sigma) and n_s < 0.990 with 99% confidence. Considering together the constraints provided by WMAP 5, (D/H)_p, baryon oscillations in the galaxy distribution, and distances to Type Ia supernovae, we arrive at the current best estimates Omega_b h^2 = 0.0224+/-0.0005 and n_s = 0.959+/-0.013.