HD molecules at high redshift: A low astration factor of deuterium in a solar-metallicity DLA system at z=2.418

TL;DR

This paper reports the detection of deuterated molecular hydrogen (HD) in a high-redshift galaxy with solar metallicity, revealing a low astration factor of deuterium and suggesting primordial gas infall, with implications for cosmology.

Contribution

It presents the first detection of HD in a high-redshift, metal-rich DLA system, providing new insights into deuterium abundance and galaxy evolution.

Findings

HD/2H2 ratio close to primordial D/H ratio

High metallicity with low deuterium astration

Potential to constrain cosmological variation of mu

Abstract

We present the detection of deuterated molecular hydrogen (HD) in the remote Universe in a damped Lyman-alpha cloud at zabs=2.418 toward the quasar SDSS J143912.04+111740.5. This is a unique system in which H2 and CO molecules are also detected. The chemical enrichment of this gas derived from ZnII and SII is as high as in the Sun. We measure N(HD)/2 N(H2)=1.5+0.6-0.4 x 10^-5, which is significantly higher than the same ratio measured in the Galaxy and close to the primordial D/H ratio estimated from the WMAP constraint on the baryonic matter density Omega_b. This indicates a low astration factor of deuterium that contrasts with the unusually high chemical enrichment of the gas. This can be interpreted as the consequence of an intense infall of primordial gas onto the associated galaxy. Detection of HD molecules at high-z also opens the possibility to obtain an independent constraint on the cosmological-time variability of mu, the proton-to-electron mass ratio.