New lensed quasars from the MUSCLES survey
  Gravitational lens systems containing lensed quasars are important as
cosmological probes, as diagnostics of structural properties of the lensing
galaxies and as tools to study the quasars themselves. The largest lensed
quasar sample is the SDSS Quasar Lens Search, drawn from the Sloan Digital Sky
Survey (SDSS). We are attempting to extend this survey using observations of
lens candidates selected from a combination of the quasar sample from the SDSS
and the UKIRT Infrared Deep Sky Survey (UKIDSS). This adds somewhat higher
image quality together with a wider range of wavelength for the selection
process. In previous pilot surveys we observed 5 objects, finding 2 lenses;
here we present further observations of 20 objects in which we find 4 lenses,
of which 2 are independently discovered in SQLS (in preparation). Following
earlier work on the combination of these two surveys, we have refined our
method and find that use of a colour-separation diagnostic, where we select for
separations between components which appear to decrease in wavelength, is an
efficient method to find lensed quasars and may be useful in ongoing and future
large-scale strong lensing surveys with instruments such as Pan-STARRS and
LSST. The new lenses have mostly high flux ratios, with faint secondaries
buried in the lensing galaxy and typically 6-10 times less bright than the
primary. Our survey brings the total number of lenses discovered in the SDSS
quasar sample to 46, plus 13 lenses already known. This is likely to be up to
60-70% of the total number of lensed quasars; we briefly discuss strategies by
which the rest might be found.
