1999A&A...349L..13M

A high-resolution, high signal-to-noise HIRES-Keck spectrum of APM 08279+5255 reveals a feature in the HI Lyα profile of the z_abs=3.514 absorber at the expected position of the corresponding DI Lyα line. The absorber shows a relatively simple velocity structure, with a major component detected in several metallic lines including CII, CIV, SiII, SiIII and Si IV. Modeling of the hydrogen column density with the minimum number of components yields (D)/(H)≃1.5x10^–5. However, a more complex structure for the hydrogen cloud with somewhat ad hoc components would allow a higher (D)/(H). The system has a very low metallicity with [Si/H]≃-3.5 and [C/H]≃-4.0 and is therefore representative of essentially unprocessed material, with a deuterium abundance close to the primordial value. The present analysis favours the low D/H value of (D)/(H)=3.39±0.25x10^–5 measured towards QSO 1009+2956 and QSO 1937-1009 (Burles & Tytler, ApJ...499..699B, 1998ApJ...507..732B) as the fiducial value of deuterium at high redshift.