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Astron. Astrophys. 340, 381-383 (1998)

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1. Introduction

The damped Ly[FORMULA] Absorption Systems (DLAS), detected in the spectra of high redshift quasars are characteristic of large neutral hydrogen column densities, and were first thought to arise in protogalactic disks (Wolfe et al. 1986). This vision has recently evolved with the detection of low redshift systems for which optical identification of the absorber could be performed (Steidel et al. 1994, Le Brun et al. 1997, Rao & Turnshek 1998). It appears in fact that all morphological types of galaxies are likely to give rise to such absorptions, and it becomes possible to study in detail the characteristics of the interstellar medium of these galaxies (absorption line analysis gives information on metallicity, ionization level, velocity structure...), coupled to their morphological type. Therefore, these DLAS are very powerful tools for studying the evolution of galaxies as regards the gaseous content, metallicity and star formation history: the absorbing gas detected in the galaxies is at the origin of stars, and the evolution of its amount gives clues for star formation rate estimates vs. cosmic time (see e.g Lanzetta et al. 1995).

However, in the redshift interval [FORMULA] (which covers up to 77% of the age of the Universe), only very few DLAS are known: 1 from the HST "QSO Absorption Lines Key Project" (Jannuzi et al. 1998), 2 from the IUE QSO survey (Lanzetta et al. 1995), and 7 inferred from the properties of metal lines and/or 21 cm absorption, and confirmed a posteriori with HST spectroscopy (Boissé et al. 1998). As a result of a HST UV spectroscopic survey of strong Mg II systems, Rao & Turnshek (1998) have increased the sample with 12 new absorbers, but there is anyway a clear need of more absorbers to sample correctly the full properties of the gas vs. galaxy morphological type, abundance, etc.

It as recently been shown that the presence of an absorbing galaxy close to a quasar sightline may induce a bias in the optical magnitude-limited samples of quasars (for example, the dust contained in the galaxy may lead to a substantial extinction of the quasar, Boissé et al. 1998), and it is therefore important to investigate different ways of selection for the quasars. In this context, we present our analysis of a UV-selected quasar spectrum displaying strong and partially resolved absorption lines by the MgII doublet at a redshift of [FORMULA].

Given the scarcity of so strong absorption features in known QSOs as mentioned above, we have searched successfully for other metal absorption lines. In this paper, we briefly present the available data in Sect. 2. Preliminary analysis of the properties of the absorption system is given in Sect. 3, leading to the conclusion that it is very likely a new candidate to the DLAS sample that consequently deserves further spectroscopic and imaging observations at higher resolution, and towards more UV wavelengths. We also emphasize the high efficiency of space UV experiments for identifying the [FORMULA] DLAS.

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© European Southern Observatory (ESO) 1998

Online publication: November 9, 1998
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