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Issue A&A
Volume 370, Number 2, May I 2001
Page(s) 426 - 435
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20010217



A&A 370, 426-435 (2001)
DOI: 10.1051/0004-6361:20010217

UVES observations of a damped Ly$\alpha$ system at $\mathsf{{\vec z}_{abs} = 4.466}$ towards the quasar APM BR J0307-4945

M. Dessauges-Zavadsky1, 2, S. D'Odorico1, R. G. McMahon3, P. Molaro4, C. Ledoux1, C. Péroux3 and L. J. Storrie-Lombardi5

1  European Southern Observatory, Karl-Schwarzschildstr. 2, 85748 Garching bei München, Germany
2  Observatoire de Genève, 1290 Sauverny, Switzerland
3  Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
4  Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, 34131 Trieste, Italy
5  SIRTF Science Center, California Institute of Technology, MS 100-22, Pasadena, CA, USA

(Received 14 September 2000 / Accepted 2 February 2001)

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 $z_{\rm em} = 4.73$ obtained with UVES on the 8.2 m VLT Kueyen telescope. We focus our analysis on a damped Ly$\alpha$ (DLA) system at $z_{\rm abs} = 4.466$ with a neutral hydrogen column density N(HI) $= (4.68 \pm 0.97) 10^{20}$ 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 $\approx$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] $=-3.07\pm 0.15$, [O/H] $=-1.63\pm 0.19$, [Al/H] $=-1.79\pm 0.11$, [Si/H] $=-1.54\pm 0.11$, [Fe/H] $=-1.97\pm 0.19$, [C/H] > -1.63 and [Ni/H] < -2.35. The derived high metallicity, ~1/90 solar, shows that this very young absorber ($\leq$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.


Key words: cosmology: observations -- galaxies: abundances -- galaxies: evolution -- quasars: absorption lines

Offprint request: M. Dessauges-Zavadsky, mdessaug@eso.org

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