Fakultäten » Mathematisch-naturwissenschaftliche Fakultät » Physik-Institut » Prof. Dr. Philippe Jetzer » Jetzer

Completed research project

Title / Titel Galaxy clusters Knowledge of the intrinsic shape of galaxy clusters (2010)
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Summary / Zusammenfassung Galaxy clusters Knowledge of the intrinsic shape of galaxy clusters is very important in investigating cosmic structure formation and astrophysical processes. In fact, the intrinsic structure directly suggests how material aggregates from large-scale perturbations and also contains evidence about the nature and mechanisms of interaction of baryons and dark matter, since processes such as virialization, dissipation or gas cooling tend to make systems more spherical, especially in the inner regions. Our group is actively working in this eld.

The over-concentration problem of strong lensing clusters (Ph. Jetzer, M. Lubini, M. Sereno) The  cold dark matter paradigm predicts that galaxy clusters follow an universal mass density pro le and t a well de ned mass-concentration relation, with lensing clusters being preferentially triaxial haloes elongated along the line of sight. Oddly, recent strong and weak lensing analyses of clusters with a large Einstein radius suggested those haloes to be highly over-concentrated. We investigated what intrinsic shape and orientation an halo should have to account for both theoretical predictions and observations [4]. We considered a sample of 10 strong lensing clusters. We rst measured their elongation assuming a given mass-concentration relation. Then, for each cluster we found the intrinsic shape and orientation which are compatible with the inferred elongation and the measured projected ellipticity. We distinguished two groups. The rst one (nearly one half) seems to be composed of outliers of the mass-concentration relation, which they would t only if they were characterised by a lamentary structure extremely elongated along the line of sight, that is not plausible considering standard scenarios of structure formations. The second sample supports expectations of N-body simulations which prefer mildly triaxial lensing clusters with a strong orientation bias.

Multi-wavelength strong lensing analysis of baryons and dark matter in dynamically active clusters (Ph. Jetzer, M. Lubini, M. Sereno) We completed our strong lensing analysis of the galaxy cluster AC 114 [18]. With respect to our rst proposal of a multi-wavelength lensing method exploiting both optical and Xray observations, we employed a more powerful Bayesian approach for model comparison. The dark matter distribution in the cluster turned out to be in remarkable agreement with predictions from N-body simulations.

Determining cosmological parameters with strong lensing (Ph. Jetzer, M. Lubini, M. Sereno) Precision cosmology era requires independent methods to probe the matter/energy content of the Universe. We are developing a statistical strong lensing approach to probe the cosmological parameters exploiting multiple redshift image systems behind massive galaxy clusters. Our method relies on non-parametric mass inversion of galaxy clusters, which provides an unbiased estimate of the cosmological parameters. We consider the statistical dispersion of the mass distribution to obtain information about the assumed cosmological model. By sampling the cosmological parameter space and employing a Bayesian approach for model comparison, we will be able to infer the probability distributions of the cosmological parameters. We are now testing the method and re ning the statistical tools on a sample of synthetic clusters.
Project leadership and contacts /
Projektleitung und Kontakte
Prof Philippe Jetzer (Project Leader)  
Mario Lubini  
Dr Mauro Sereno  
Funding source(s) /
Unterstützt durch
Universität Zürich (position pursuing an academic career), Others
Duration of Project / Projektdauer Jan 2010 to Dec 2010