UVES Observations of QSO 0000−2620: Oxygen and Zinc Abundances in the Damped Lyα Galaxy at z abs = 3.3901

Abstract

Observations of the QSO 0000-2620 with the Ultraviolet-Visual Echelle Spectrograph at the 8.2 m ESO Kueyen telescope are used for abundance analysis of the damped Lyα system at zabs = 3.3901. Several oxygen lines are identified in the Lyα forest, and a measure for the oxygen abundance is obtained at [O/H] = -1.85 ± 0.15 by means of the unsaturated O I λ925 and O I λ950 lines. This represents the most accurate O measurement in a damped Lyα galaxy so far. We have also detected Zn II λ2026 and Cr II λλ2056, 2062 redshifted at ≈8900 Å and found abundances [Zn/H] = -2.07 ± 0.10 and [Cr/H] = -1.99 ± 0.09. Furthermore, previous measurements of Fe, Si, Ni, and N have been refined, yielding [Fe/H] = -2.04 ± 0.09, [Si/H] = -1.90 ± 0.08, [Ni/H] = -2.27 ± 0.09, and [N/H] = -2.68 ± 0.12. The abundance of the nonrefractory element zinc is the lowest among the damped Lyα systems, showing that the associated intervening galaxy is indeed in the early stages of its chemical evolution. The fact that the Zn abundance is identical to that of the refractory elements Fe and Cr suggests that dust grains have not formed yet. In this damped Lyα system the observed [O, S, Si/Zn, Fe, Cr] ratios, in whatever combination are taken, are close to solar (i.e., 0.1-0.2 dex) and do not show the [α-element/Fe] enhancement observed in Milky Way stars of comparable metallicity. The observed behavior supports a galaxy evolution model characterized by either episodic or low star formation rate rather than a Milky Way-type evolutionary model.