Deuterium to hydrogen towards QSO 1009+2956 from a mesoturbulent model

Abstract

We present a new analysis of the deuterium absorption at z = 2.504 towards the quasar Q1009+2956 using the mesoturbulent model which accounts for possible correlations in the large scale velocity field. We obtain a slightly higher deuterium-to-hydrogen ratio D/H = (3.5 - 5.0)*10^{-5} as compared with the recent measurement D/H = (3.3 - 4.5)*10^{-5} (68% C.L.) performed by Burles & Tytler (1998b) using the usual microturbulent approximation which assumes that the velocity field is uncorrelated. Other mesoturbulent calculations of the D-abundances at z = 3.572 towards Q1937--1009 and at z = 0.701 towards Q1718+4807 (the systems showing `low' and possibly `high' D/H values, respectively, in the microturbulent approaches) agree with the present one within the errors of measurements. Thus, the mesoturbulent analysis does not reveal any spatial variations of D/H and supports the standard homogeneous model of big bang nucleosynthesis.