UVES observations of a damped Lyɑ system at z_(abs) = 4.466 towards the quasar APM BR J0307-4945

Abstract

We present the first high-resolution (6.2 to 7.7 km s^(-1) FWHM) spectra of the APM BR J0307-4945 quasar at z_(em) = 4.73 obtained with UVES on the 8.2 m VLT Kueyen telescope. We focus our analysis on a damped Lyɑ (DLA) system at z_(abs) = 4.466 with a neutral hydrogen column density N(HI) = (4.68 ± 0.97) 10^(20) cm^(-2). It is the most distant DLA system known to the present date, observed when the age of the universe was only 1.3 Gyr. It shows complex low- and high-ionization line profiles spanning ≈240 and 300 km s^(-1) in velocity space respectively. We derive accurate abundances for N, O, Al, Si and Fe, and place a lower limit on C and an upper limit on Ni: [N/H] =-3.07 ± 0.15, [O/H] =-1.63 ± 0.19, [Al/H] =-1.79 ± 0.11, [Si/H] =-1.54 ± 0.11, [Fe/H] =-1.97 ± 0.19, [C/H] > -1.63 and [Ni/H] < -2.35. The derived high metallicity, ~1/90 solar, shows that this very young absorber (≤ 1.3 Gyr) has already experienced a significant metal enrichment. The [O/Si] ratio is nearly solar suggesting a limited amount of dust, the relative [Si, O/Fe] abundance ratios show a similar enhancement as observed in the Milky Way stars with comparable metallicities, and the [N/O] ratio is very low. All these results point to an enrichment pattern dominated by type II supernovae which suggests a Milky Way type evolutionary model.

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