The 2dF gravitational lens survey
Daniel J. Mortlock, Darren S. Madgwick, Ofer Lahav, PASA, 18 (2), in press.
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The 2dF galaxy redshift survey

The 2dF GRS (e.g., Folkes et al. 1999; Cole et al. 2001) is, formally, a spectroscopic survey of $\sim 2.5 \times 10^5$ extended images, all of which have isophotal magnitudes brighter than $B_{\rm J} = 19.45$. The data are obtained using the 2dF instrument, an automatically-configurable multi-fibre spectrograph on the Anglo-Australian Telescope (AAT). The $\sim 10^5$ spectra obtained so far have a resolution of about 10 Å, and cover the range from $\sim 3700$ Å to $\sim 8100$ Å. Whilst the wavelength calibration is excellent, there have been some problems with the flux calibration, and so continuum levels remain quite uncertain. The spectra are typically the result of 45-min integrations, and so the signal-to-noise ratio in each pixel is between $\sim 10$ and $\sim 20$ for an object at the survey limit.

It is expected that $\sim 95$ per cent of the objects selected for the survey will be local galaxies, with the remainder being mainly misidentified Galactic stars. However a few of the survey galaxies will be multiply-imaging background quasars, and, if the quasars are sufficiently bright, should be identifiable as gravitational lenses. Two main questions present themselves at this point: how many lenses might be detectable in these spectra, and what is the best way to find any lenses that might be present? The answers are related, in so far as any given search method is linked to the effective ``depth'' of the lens survey, but it is possible to obtain an estimate of the number of lenses without fully understanding how to find them.

Next Section: Lens statistics
Title/Abstract Page: The 2dF gravitational lens
Previous Section: Introduction
Contents Page: Volume 18, Number 2