The Metal Systems in the Line of Sight Towards GB1759+7539

Abstract

Observations of the high-redshift QSO GB1759+7539 (z em = 3.05) have been obtained with HIRES on the Keck 10m telescope. The spectrum has a resolution of FWHM=7kms-1, a typical S/N ~ 25 in the Lyα forest region and ~ 60 long-ward of the Lya emission. Twelve heavy-element absorption systems were identified, including damped Lyman-alpha (DLA) systems at z abs=2.62 and 2.91. The C, N, O, Al, Si, P, S, Mg, Fe, and Ni absorption features of these systems were studied, and the elemental abundances calculated for the weak unsaturated lines. The systems have metallicities of z 2.62 ≃ 1/20Z ⊙ and z 2.91 ≃ 1/45Z ⊙ (see Fig. 1). Both systems appear to have a low dust content. They show an over-abundance of a-elements relative to Fe-peak elements, and an under-abundance of odd atomic number elements relative to even. N was observed in the zz abs=2.62 system, and found to be under-abundant relative to O, in line with the time delay model of primary N production. C II* was also seen, allowing us to determine an upper limit to the cosmic microwave background temperature at z=2.62 of TCMB < 12.0K.