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Astron. Astrophys. 352, L51-L56 (1999)

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1. Introduction

Within standard Cold Dark Matter scenarios the formation of galaxies is a hierarchical and biased process. Large galaxies are thought to be assembled through the merging of smaller systems, and the most massive objects will form in over-dense regions, which will eventually evolve into the clusters of galaxies (Kauffmann et al. 1999). It is therefore important to find and study the progenitors of the most massive galaxies at the highest possible redshifts.

Radio sources are convenient beacons for pinpointing massive elliptical galaxies, at least up to redshifts [FORMULA] (Lilly & Longair 1984; Best, Longair & R"ottgering 1998). The near-infrared `Hubble' [FORMULA] relation for such galaxies appears to hold up to [FORMULA], despite large K-correction effects and morphological changes (Lilly and Longair 1984; van Breugel et al. 1998, 1999). This suggests that radio sources may be used to find massive galaxies and their likely progenitors out to very high redshift.

While optical, `color-dropout' techniques have been successfully used to find large numbers of `normal' young galaxies (without dominant AGN) at redshifts surpassing those of quasars and radio galaxies(Weymann et al. 1998), the radio and near-infrared selection technique has the additional advantage that it is unbiased with respect to the amount of dust extinction. High redshift radio galaxies (HzRGs) are therefore also important laboratories for studying the large amounts of dust (Dunlop et al. 1994; Ivison et al. 1998) and molecular gas (Papadopoulos et al. 1999), which are observed to accompany the formation of the first forming massive galaxies.

Using newly available, large radio surveys we have begun a systematic search for [FORMULA] HzRGs to be followed by more detailed studies of selected objects. In this Letter, we present deep intermediate resolution VLT/FORS1 spectroscopy of TN J1338-1942 which, at [FORMULA], was the first [FORMULA] radio galaxy discovered in the southern hemisphere (De Breuck et al. 1999a), and is one of the brightest and most luminous Ly[FORMULA] objects of its class.

In § 2, we describe the discovery and previous observations of TN J1338-1942. In § 3 we describe our VLT observations, and in § 4 we discuss some of the implications of our results. Throughout this paper we will assume [FORMULA] km s-1Mpc-1, [FORMULA]=0.15, and [FORMULA]. At [FORMULA], this implies a linear size scale of 7.5 kpc/arcsec.

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© European Southern Observatory (ESO) 1999

Online publication: November 23, 1999