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Issue A&A
Volume 449, Number 1, April I 2006
Page(s) 33 - 39
Section Cosmology (including clusters of galaxies)
DOI 10.1051/0004-6361:20053910

A&A 449, 33-39 (2006)
DOI: 10.1051/0004-6361:20053910

Kinematics and star formation activity in the z $\mathsf{_{abs}}$ = 2.03954 damped Lyman- $\mathsf{\alpha}$ system towards PKS 0458-020

J. Heinmüller1, 2, 3, P. Petitjean1, 4, C. Ledoux5, S. Caucci1 and R. Srianand6

1  Institut d'Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
2  Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
    e-mail: janine@ari.uni-heidelberg.de
3  Astrophysik, Universität Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany
4  LERMA, Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France
5  European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago, Chile
6  IUCAA, Post Bag 4, Ganesh Khind, Pune 411 007, India

(Received 25 July 2005 / Accepted 16 November 2005)

Abstract
We present UVES observations of the log N(H I) = 21.7 damped Lyman-$\alpha$ system at $z_{\rm abs}$ = 2.03954 towards the quasar PKS 0458-020. H I Lyman-$\alpha$ emission is detected in the center of the damped Lyman-$\alpha$ absorption trough. Metallicities are derived for Mg II, Si II, P II, Cr II, Mn II, Fe II and Zn II and are found to be $-1.21\pm0.12$, $-1.28\pm0.20$, $-1.54\pm0.11$, $-1.66\pm0.10$, $-2.05\pm0.11$, $-1.87\pm0.11$, $-1.22\pm0.10$, respectively, relative to solar. The depletion factor is therefore of the order of [Zn/Fe] = 0.65. We observe metal absorption lines to be blueshifted compared to the Lyman-$\alpha$ emission up to a maximum of ~100 and 200 km s-1 for low and high-ionization species respectively. This can be interpreted either as the consequence of rotation in a large (~7 kpc) disk or as the imprint of a galactic wind. The star formation rate (SFR) derived from the Lyman-$\alpha$ emission, 1.6 $M_{\odot}$ yr-1, is compared with that estimated from the observed C II* absorption. No molecular hydrogen is detected in our data, yielding a molecular fraction ${\rm log}\,f$ < -6.52. This absence of H2 can be explained as the consequence of a high ambient UV flux which is one order of magnitude larger than the radiation field in the ISM of our Galaxy and originates in the observed emitting region.


Key words: cosmology: observations -- galaxies: abundances -- galaxies: quasars: absorption lines -- galaxies: quasars: individual: PKS 0458-020 -- galaxies: kinematics and dynamics

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