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TP leader: Stella Seitz

Gravitational lensing has proved to be a unique tool to measure the (total) projected mass of galaxies and galaxy clusters on radial scales from kiloparsecs to megaparsecs with a minimal set of assumptions. In particular, its robustness is extremely useful to address the relationship between dark and luminous matter for these systems. Moreover, the lensing configuration (radii of einstein rings) depends on diameter distances to the lens and source and thus on the adopted cosmological model in a purely geometrical way. Therefore, lensing provides a method to estimate the values of the cosmological parameters, offering an important alternative test for the $\Lambda$CDM concordance model.

In this project, we aim at selecting, observing (if necessary), and studying in detail a few dozens of already known gravitational lensing systems with early-type galaxies acting as deflectors. To develop these systems into cosmological probes one only needs to measure the steepness of the density profile between half and one effective radius, because this determines the angular sizes for the Einstein radii of sources at different redshifts.

First, we plan to do this for about 20 such SLACS lensing systems, which are suited due their complex extended or multiple sources (at the same redshift) to precicely constrain the mass density slope around the effective radius.

The second aim of this project is to analyze the upcoming
BOSS/SDSS-III data set to increase the number of lensing systems, so
that our method to probe the geometry of the universe can become
competitive to the more classical ones in TR 33. The access to the
SDSS-III spectroscopic data is secured by the membership of MPE in the
German SDSS-III consortium.

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