The Deuterium Abundance at [FORMULA][F]z=0.701[/F][/FORMULA][CLC][ITAL]z[/ITAL][/CLC] = 0.701 toward QSO 1718+4807

David Tytler, Scott Burles, Limin Lu, Xiao-Ming Fan, Arthur Wolfe, Blair D. Savage
1999 Astronomical Journal  
We present constraints on the deuterium to hydrogen ratio (D/H) in the metal-poor gas cloud at redshift $z=0.701$ towards QSO 1718+4807. We use new Keck spectra in addition to Hubble Space Telescope (HST) and International Ultraviolet Explorer (IUE) spectra. We use an improved redshift and a lower \HI column density to model the absorption. The HST spectrum shows an asymmetric Lyman-$\alpha$ (\lya) feature which is produced by either \HI at a second velocity, or a high abundance of D. Three
more » ... nce of D. Three models with a single simple H+D component give $8 \times 10^{-5} < D/H < 57 \times 10^{-5}$ (95%), a much larger range than reported by Webb et al (1997a,b). A more sophisticated velocity distribution, or a second component is necessary for lower D/H. With two components, which could be a part of one absorbing structure, or separate clouds in a galaxy halo, we find $D/H < 50 \times 10^{-5}$. We do not know if this second component is present, but it is reasonable because 40 -- 100% of absorption systems with similar redshifts and \HI column densities have more than one component.
doi:10.1086/300715 fatcat:oryglsk2ordl5ibzo4pynla2y4