The D/H Ratio at z = 3.57 toward Q1937–1009

Deuterium abundance remeasurements by Burles & Tytler yielded D/H=(3.3±0.3)×10−5 and the robust upper limit D/H<3.9×10−5 from the za=3.572 system toward Q1937-1009. In this new analysis, Burles & Tytler adopted multicomponent microturbulent models, together with the possibility of varying the local continuum level freely around each H I line to improve the fit. However, the procedure failed to fit D Lyβ adequately without recourse to an additional H Lyα contamination at the position of D Lyβ. We show that this obstacle may be successfully overcome within the framework of the mesoturbulent model, which accounts (in contrast to the microturbulent approximation) for a correlated structure of the large-scale velocity field. Using the same observational data and the original continuum as determined by Tytler et al., we obtained good fits. The one-component mesoturbulent models provide D/H in the range ≃(3.5-5.2)×10−5 and N(H I) ≃ (5.3-7.0)×1017 cm−2 (95% confidence). This result is consistent with that found by us from the za=2.504 and za=0.701 systems toward Q1009+2956 and Q1718+4807, respectively. The range for D/H common to all three analyses is D/H ≃ (4.1-4.6)×10−5. This value is consistent with standard big bang nucleosynthesis if the baryon-to-photon ratio, η, is in the range 4.2×10−10≲η≲4.6×10−10, implying 0.0155≲Ωbh2100≲0.0167.