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Astron. Astrophys. 343, L35-L39 (1999)

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1. Introduction

Einstein-ring gravitational lens images should be much more common at optical wavelengths than at radio wavelengths (Miralda-Escudé and Lehár 1992), but so far all but one of the known Einstein rings have been discovered by radio techniques. The exception is 0047-2808 (Warren et al. 1996a) where a high-redshift [FORMULA] star-forming galaxy, with strong Ly[FORMULA] emission at 5589Å, is lensed by a massive early-type galaxy at [FORMULA]. We are engaged in a survey to detect similar systems (Warren et al. 1996b). The search strategy is to identify anomalous emission lines (Ly[FORMULA] from star-forming galaxies at [FORMULA]) in the spectra of a large sample of distant early-type galaxies at [FORMULA]. This has the advantage that by the very nature of the identification procedure the redshifts of both the source and deflector are obtained and so the full lensing geometry is known. In addition, because the sources are extended the resulting images, rings or arcs, offer the prospect of providing powerful constraints on the mass distribution in the deflecting galaxies (Kochanek 1995). Finally, because of the magnification, it is possible to study these very faint sources both spectroscopically (Warren et al. 1998) and morphologically, resolving angular scales much smaller than is possible for unlensed objects. The latter prospects are of particular interest because the sources are similar to but fainter than the population of high-redshift star-forming objects identified by Steidel and coworkers (Steidel et al. 1996), and cannot presently be studied in any other way. In this paper we present VLT UT1 broad- and narrow-band imaging, together with UKIRT K-band imaging of 0047-2808.

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© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999