Introduction

It is possible to discover gravitational lenses spectroscopically by searching for quasar emission lines in the spectra of local galaxies. This is the only way to find lenses with low-redshift deflectors; these are particularly valuable as the lens galaxies can be studied in great detail and the timescales for microlensing are short enough to permit a range of interesting measurements (Mortlock & Webster 2000 and references therein). Kochanek (1992) and Mortlock & Webster (2000) calculated the expected event rate, and several tens of spectroscopic lenses should be forthcoming from the current generation of galaxy redshift surveys (GRSs).¹

The first large GRS, the Center for Astrophysics (CfA) survey (Geller & Huchra 1989), resulted in the discovery of the lens Q 2237+0305 (Huchra et al. 1985), although it was an essentially serendipitous event. There have been no other quasar lenses discovered in this manner, but several searches for lensed emission line galaxies have been undertaken. The only confirmed spectroscopic discoveries were the two Einstein rings found by Warren et al. (1996) and Hewett et al. (1999) in their sample of large elliptical galaxies. Even though there are only several hundred galaxies in the survey, the regularity of their spectra is such that a very sensitive search for discrepant emission lines is possible (Willis et al. 2001); several more candidates have been identified and are awaiting re-observation. Hall et al. (2000) also announced the identification of several candidate lenses in the Canadian Network for Observational Cosmology (CNOC) GRS (Yee et al. 2000), although these too are yet to be confirmed. The next generation of galaxy survey is exemplified by the Sloan Digital Sky Survey (SDSS; York et al. 2000) which, with galaxy spectra, should yield at least 50 spectroscopic lenses (not to mention the several hundred lenses expected to be resolved in the imaging survey). The SDSS has only recently got under way, but, at the time of writing, over 5 x 10⁴ spectra have been obtained, and the pipeline reduction software should be able to select lens candidates with some reliability, although none have been announced so far.

This paper details the beginnings of a lens survey based on the spectra taken as part of the largest existing galaxy sample, the 2 degree Field (2dF) GRS (Section 2). After a brief discussion of the lens statistics (Section 3), the possible spectral analysis methods are examined (Section 4). These points are summarised in Section 5.

© Copyright Astronomical Society of Australia 1997