Extragalactic Astrophysics

The research group of Tim Schrabback investigates research questions within the field of extragalactic astrophysics and cosmology, e.g. regarding the nature of dark energy. It seems that this invisible and likely ubiquitous substance speeds up the cosmic expansion and dominates the energy budget in the present-day universe. However, its true physical nature is still unclear. To help answer this and other cosmological questions, the research group is analysing large astronomical data sets.

One of the primary astrophysical tools used by the group is weak gravitational lensing: As predicted by Einstein's general relativity, the observed images of distant galaxies get distorted when their light-rays pass through the gravitational field of the foreground matter distribution. These distortions can be studied statistically by analysing the images of large sets of background galaxies. Such measurements enable the researchers to reconstruct the mass distribution in the foreground (dominated by the invisible dark matter), weigh cosmological objects such as galaxies and galaxy clusters, and constrain the cosmological model.

One research focus of the group is the use of gravitational lensing measurements to constrain galaxy cluster masses. Such measurements are of critical importance in order to derive accurate cosmological constraints from galaxy cluster surveys. For these analyses members of the group work as part of international collaborations (South Pole Telescope, Kilo Degree Survey, eROSITA) and additionally analyse observational data from the Hubble Space Telescope and the Very Large Telescope of the European Southern Observatory.

As a further central research focus the group is working on preparations for gravitational lensing measurements with imaging data from the upcoming ESA Mission Euclid.



Image of the super-massive galaxy cluster RCS2J232727.7-020437 (redshift 0.70, angular diameter distance approximately 4.9 billion light-years) obtained with the Advanced Camera for Surveys onboard the NASA/ESA Hubble Space Telescope (blue and green image channel in the centre) and the HAWK-I imager at the Very Large Telescope of the European Southern Observatory (red image channel). The contours show the weak lensing-reconstructed mass distribution of the cluster (dominated by the invisible dark matter). In addition to the yellow-orange cluster galaxies, the full image (click on the thumbnail) reveals several strongly distorted multiple-image systems of distant background galaxies (strong gravitational lensing).

Source: Schrabback et al. 2018, A&A 610, 85.



 Tim Schrabback

Head of the Research Group

Univ.-Prof. Dr. Tim Schrabback
Tel. +43 512 507-52010

Administrative Assistant

Julia Mönnich
Tel. +43 512 507-52091

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