It looks like you're using an Ad Blocker.
Please white-list or disable AboveTopSecret.com in your ad-blocking tool.
Some features of ATS will be disabled while you continue to use an ad-blocker.
In addition to the rare cluster lenses that will be found in the LSST survey, the survey images will produce at least an order of magnitude increase in galaxy-scale lenses. Our simulations predict that the final stacked data set will contain approximately 5000 detectable cases of a background galaxy being multiply-imaged by a foreground system. In addition, we predict that there will be ~150 systems in which the lensed objects are AGN or quasars and the lens system can be identified in a one-epoch image with an integration time of 20 seconds (assuming seeing of 0.7 arcsec). This number increases to ~1500 systems if the seeing is 0.4 arcsec. More generally, with shapes and redshifts of billions of source galaxies LSST will measure the compact dark matter distribution on these scales with precision.
The source population numbers to the survey limiting magnitude may be estimated from the Hubble Deep Field (HDF), suggesting some 3 x 105 galaxies per square degree at z > 1 (Metcalfe et al. 2001, Fernandez-Soto et al. 1999). We may reasonably expect of order 107 multiple image systems to be present in the survey, using a lensing rate of 10-3 as found in the CLASS survey (Browne et al. 2003); however, only a fraction of these lenses will be identified by LSST alone. The lensing cross-section is dominated by massive elliptical galaxies at redshifts 0.3 < z < 1 (e.g. Fukugita & Turner 1991, Blandford et al. 2001); again from the HDF, we may expect approximately 10,000 such "clean lens" galaxies per square degree, providing about 30 square degrees of lensing cross-section in the whole survey. By targeting these ellipticals and searching for achromatic excesses, a substantial fraction of these lenses may be detected; note the great importance of multi-color LSST imaging in this task. The resulting large sample of wide separation lenses will allow high precision statistical tests of the level of small-scale and non-axisymmetric structure in galaxies and groups.
The prospect of discovering a significant number of higher-order catastrophe lenses in the LSST sample is an exciting one: as an example, the "quintuple quasar" lens system has six lensed images, with the lens model predicting two more (Winn et al. 2003, Keeton & Winn 2003). Such multiple image systems will provide much information on lens galaxy structure, while the very high magnifications attainable will provide us with a very powerful "cosmic telescope." The LSST optical data on sources observed in this way will provide very important complementary information to that available in similar scale low cadence surveys across the rest of the electromagnetic spectrum, including those by EXIST in the X-ray band and the Square Kilometer Array in the radio.