HD molecules at high redshift^*

A low astration factor of deuterium in a solar-metallicity DLA system at z = 2.418

¹ Institut d'Astrophysique de Paris, CNRS - Université Pierre et Marie Curie, 98bis Bd Arago, 75014 Paris, France e-mail: [noterdaeme;petitjean]@iap.fr
² European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago 19, Chile e-mail: cledoux@eso.org
³ Inter University Centre for Astronomy and Astrophysics, Post Bag 4, Ganesh Khind, Pune 411 007, India e-mail: anand@iucaa.ernet.in
⁴ Ioffe Physical Technical Institute, St Petersburg 194021, Russia e-mail: iav@astro.ioffe.ru

Received: 18 June 2008
Accepted: 20 September 2008

Abstract

We present the detection of deuterated molecular hydrogen (HD) in the remote Universe in a damped Lyman-α cloud at 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 Zn ii and S ii is as high as in the Sun. We measure , 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 (). 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 of obtaining an independent constraint on the cosmological-time variability of μ, the proton-to-electron mass ratio.