i have been following the rapid changes made in the feild of galaxy lensing over the last 6 months
there has been great leaps forward in the areas of detection and identification of galactic lenses
the understanding gained and the change to how we veiw the universe is massive.
this feild of reasurch has the potential to change our perception of the universe and answer some of the most paradoxical questions about
hot dark matter
cold dark matter
unusually high rotational speeds of galaxies
"missing mass" in the observable universe
halos of dark matter
the study of the different forms of lensing may be used to explain the paradoxes we encounter.
some of the galaxies we see could be "magnified" and this would make the rotational speeds incorrect for the size and mass of the galaxy we are
mass "hidden" inside these lenses would not be visable from the wrong angle of incidence and may not be detectable directly from observations and
therefore be "missing mass". only the mass at the center of the lens would be visable under specific conditions.
dark energy may be shown to be a reflection artifact from the transition behind an galaxy lense, this has the effect of showing the motion of mass in
the opposite direction to acual travel.
as we get a grip on the numbers of galaxy lenses and the numbers of reflection artifacts we may redifine the observable universe.
mass distrabution in a cluster lense
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.
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