SQLS: Overview
Gravitationally lensed quasars have proved to be a powerful tool
to explore the Universe. It serves as an ideal probe of dark matter
in galaxies and clusters, since lensing gives a robust measurement
of the projected mass inside the Einstein radius. Moreover, the
cosmological nature of lensed quasars as well as well-understood
underlying physics makes lensed quasars a unique probe of
cosmological parameters. For instance, the probability of strong
lensing is sensitive to various cosmological parameters such as
the abundance of dark energy. Time delays between multiple images
of lensed quasar systems offer a direct probe of the global Hubble
constant.
The first gravitationally lensed quasar Q0957+561 was discovered in
1979. Since then, roughly 80 lensed quasars have been discovered
with various methods applied to optical or radio data. However,
applications of these lensed quasar systems have often been limited
by the small number of lenses, in particular those identified by
homogeneous criteria: This is why large systematic surveys of
lensed quasars have been anticipated.
The SDSS Quasar Lens Search (SQLS) is aimed to discover many (~100)
lensed quasars from the large homogeneous data of
the Sloan Digital Sky
Survey (SDSS). The SDSS is an ambitious optical survey to map
1/4 of the entire sky with five broad band imaging. The SDSS also
conducts extensive spectroscopic surveys of galaxies and quasars
to make a three-dimensional map of the Universe. When completed,
the SDSS will yield a spectroscopic sample of 100,000 quasars.
Our plan of the SQLS is to take advantage of this huge
spectroscopic quasar sample to locate many lensed quasars.
We search for lensed quasars using well-studied selection algorithms,
which allows accurate estimates of lensing rates and lensing biases.
In addition, the aim of the SQLS includes the detection of rare
quasar lens events such as multiple quasars lensed by a massive
cluster of galaxies.