The D/H ratio at z=0.7 toward Q 1718+4807

Abstract

The apparent discrepancy between low and high D abundances derived from QSO spectra may be caused by spatial correlations in the stochastic velocity field. If one accounts for such correlations, one finds good agreement between different observations and the theoretical predictions for standard big bang nucleosynthesis (SBBN). In particular, we show that the H+D Lyalpha profile observed at z_a = 0.7 toward Q 1718+4807 is compatible with 4.1 10(-5) < D/H < 4.7 10(-5) . This result is consistent with our previous D/H determination for the z_a = 2.504 system toward Q 1009+2956 and, thus, supports SBBN.