Low deuterium abundance in the z(abs)=3.514 absorber towards APM 08279+5255

A high-resolution, high signal-to-noise HIRES-Keck spectrum of APM 08279+52 55 reveals a feature in the HI Ly alpha profile of the z(abs)=3.514 absorbe r at the expected position of the corresponding DI Ly alpha line. The absor ber shows a relatively simple velocity structure, with a major component de tected in several metallic lines including CII, CIV, Sill, SiIII and Si IV. Modeling of the hydrogen column density with the minimum number of compone nts yields D/H approximate to 1.5 x 10(-5) However, a more complex structur e for the hydrogen cloud with somewhat ad hoc components would allow a high er D/H. The system has a very low metallicity with [Si/H] approximate to -3 .5 and [C/H] approximate to -4.0 and is therefore representative of essenti ally unprocessed material, with a deuterium abundance close to the primordi al value. The present analysis favours the low D/H value of D/H =3.39 +/-0. 25 x 10(-5) measured towards QSO 1009+2956 and QSO 1937-1009 (Burles & Tytl er 1998a, 1998b) as the fiducial value of deuterium at high redshift.