Abstract

We report the detection of neutral deuterium in the low-metallicity damped Lyman-? system at z abs = 2.621 towards the quasar CTQ 247. Using a high signal-to-noise and high spectral resolution (R = 60 000) spectrum from the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph, we precisely measure the deuterium-to-oxygen ratio log N(D i)/N(O i) = 0.74 ± 0.04, as well as the overall oxygen abundance, log N(O i)/N(H i) =-5.30 ± 0.10 (or equivalently [O/H] =-1.99 ± 0.10 with respect to the solar value). Assuming uniform metallicity throughout the system, our measurement translates into (D/H) = (2.8 +0.8 -0.6) × 10 -5. This ratio is consistent within errors (<0.4?) with the primordial ratio, (D/H) p = (2.59 ± 0.15) × 10 -5, predicted by standard Big-Bang nucleosynthesis using the WMAP7 value of the cosmological density of baryons (100? bh 2 = 2.249 ± 0.056). The D i absorption lines are observed to be broader than the O i absorption lines. From a consistent fit of the profiles we derive the turbulent broadening to be 5.2 km s -1 and the temperature of the gas to be T = 8800 ± 1500 K, corresponding to a warm neutral medium. © 2012 ESO.