Deuterium at high redshift

Primordial abundance in the z_abs = 2.621 damped Ly-α system towards CTQ 247^⋆

P. Noterdaeme¹, S. López², V. Dumont², C. Ledoux³, P. Molaro⁴ and P. Petitjean¹

¹ CNRS-UPMC, UMR7095, Institut d’Astrophysique de Paris, 98bis bd Arago, 75014 Paris, France
e-mail: noterdaeme@iap.fr
² Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
³ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
⁴ Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34131 Trieste, Italy

Received: 21 April 2012
Accepted: 17 May 2012

Abstract

We report the detection of neutral deuterium in the low-metallicity damped Lyman-α 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 (<0.4σ) 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   Ω_bh² = 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.