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Holger Israel

Transregional Collaborative Research Centre TRR 33 -
The Dark Universe

Universität Heidelberg jointly with Universität Bonn and LMU München



Project: B6 (Bartelmann-Reiprich)

Gravitational Lensing and X-Ray Emission by Non-Linear Structures


Gravitational lensing offers three ways for studying dark matter halos and their evolution: strong lensing, which is non-linearly sensitive to the detailed mass distribution in the halo cores; weak lensing by individual halos, which allows mapping of their projected mass distribution; and weak lensing by large-scale structures, from which the lensing signal of halos can be filtered. We plan to study in this Teilprojekt the impact of dark energy on these three variants of halo lensing and possibilities to constrain dark energy by means of halo lensing.

Specifically, we intend to address three questions. First, can the counts of halos detected by weak-lensing methods be expected to be precise enough for constraining dark energy models? The lensing signal from the halos must be separated from substantial noise due to the larger-scale structure. Since some classes of dark energy models predict largely differing halo counts at redshifts z>0.5, filtering techniques for halo detection must likely be combined with, e.g., photometric redshifts to select halos in relevant redshift ranges.

Second, can X-ray selected and X-ray characterised halos be combined with weak lensing observations to identify dynamical activity in the halos? One discriminant between dark energy and LambdaCDM models is the merger rate of cluster-sized halos at redshifts between 0.5 and 1.0. While gravitational lensing detects the mass of the merging halos regardless of their physical state, their gas mass may be far from equilibrium. The discrepancy of cluster parameters from lensing and X-ray data should thus allow quantification of the dynamical activity in clusters.

Third, can the optical depth for strong gravitational lensing be used for distinguishing certain classes of dark energy models from cosmologies with cosmological constant? Increased dynamical activity in clusters with z>0.5 is expected to contribute strongly to the optical depth for strong lensing, offering a potential way to characterise the dynamical state of the cluster population at those redshifts.

Several people are involved in this project. Those directly funded by this Transregio include Holger Israel and Matteo Maturi. This Transregio is funded by the Deutsche Forschungsgemeinschaft (DFG).


Contact: Matthias Bartelmann Thomas Reiprich
Phone: +49 6221 54-4817 +49 228 73-3642
Fax: +49 6221 54-4837 +49 228 73-4022
E-Mail: mbartelmann(at) reiprich(at)