A new deuterium abundance measurement from a damped Ly-alpha system at z_abs = 3.025

Abstract

We present the first D/H measurement in a damped Ly-alpha system at z_abs = 3.025 towards QSO 0347-3819 obtained from the UVES-VLT spectra. The DLA absorber has a metallicity of [Zn/H] = -1.25 and a relatively simple velocity structure, with two dominating components detected in several metal lines. The hydrogen Lyman series can be followed down to Ly12 thanks to the high UV-Blue efficiency of UVES. The best fit of the Lyman series lines, and in particular of Ly5, Ly8, Ly10 and Ly12, relatively free of local contamination, is obtained when the DI absorption is included in the two main components. The measured deuterium column density yields D/H = (2.24+/-0.67) 10^{-5} close to other low D/H values from Lyman limit systems. The corresponding values for the baryon to photon ratio and the baryon density derived from D/H are eta = 6 10^{-10} and Omega_b h^2 = 0.023 respectively.