A high-resolution , high signal-to-noise HIRES-Keck spectrum of APM 08279+5255 reveals a feature in the HI Ly \alpha profile of the z _ { abs } =3.514 absorber at the expected position of the corresponding DI Ly \alpha 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 \frac { D } { H } \approx 1.5 \times 10 ^ { -5 } .
However , a more complex structure for the hydrogen cloud with somewhat ad hoc components would allow a higher \frac { D } { H } .
The system has a very low metallicity with [ Si/H ] \approx - 3.5 and [ C/H ] \approx - 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 \frac { D } { H } = 3.39 \pm 0.25 \times 10 ^ { -5 } measured towards QSO 1009+2956 and QSO 1937-1009 ( Burles & Tytler 1998a , 1998b ) as the fiducial value of deuterium at high redshift .