Statistical Measurement of Primordial Deuterium Abundance

Abstract

Lyman series absorption features and corresponding metal lines in three high-resolution quasar spectra are fitted in the standard way with thermally broadened discrete redshift components. A candidate sample is assembled, of 10 velocity components in 7 separate complexes, which display features attributable to deuterium. Three of these components in 2 complexes were previously published; the fits to the seven others are described here in detail. To estimate the contamination of this sample by hydrogen ``interlopers'', a control sample of ``pretendium'' candidates is assembled from the same data, and in the same way in all respects but one: the control sample candidates are drawn from the red side of hydrogen absorbers, rather than the blue side where the deuterium feature appears. The control sample is therefore drawn from a population with the same statistical properties as the plausible interlopers, including their joint correlationsin velocity, column density and width. The properties of the two samples are compared statistically, using the Doppler parameters and column densities from the line fits, and are found to be significantly different. The D candidates have narrower Doppler parameters, consistent with the deuterium identification. The column densities of the D sample (but not the P sample) are consistent with a universal cosmic abundance; the weighted mean abundance for the new candidates presented here is $ < log (D/H) > = -3.75 \pm 0.51 $.