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My scientific work focuses on the evolution of galaxies over cosmic
time scales - billions of years. Galaxies consist of billions of stars, gas,
dust and dark matter. The latter is not observable directly (hence its
name) but only indirectly via the gravity it enforces on visible matter
or light. A huge variety of observations show that the major mass
fraction of all galaxies consists of dark matter. There are several types
of galaxies, e.g. elliptical galaxies and spiral galaxies like our own
Milky Way. For my observations, I am utilizing instruments like the
Hubble Space Telescope of the Very Large Telescope operated by the
European Southern Observatory on Cerro Paranal, Chile.
One of my main research areas is the influence of
: observations have shown that the properties of
a given galaxy (like its morphology, gas content and so forth) depend on
whether it is isolated or resides in a galaxy cluster. Clusters
can consist of up to thousands of galaxies. A spellbinding observational
finding is that spiral galaxies that are falling into galaxy clusters
from the surrounding field can dramatically change their morphology,
undergoing a transformation
A range of observations, including work done by our own research group, indicate that spiral galaxies (left) can be transformed into so-called lenticular galaxies (right) via a combination of physical processes occurring in galaxy clusters
(credits: NASA, ESA, Hubble Heritage, John Kormendy).
Another topic I am working on are
of spiral galaxies. The term scaling relations
refers to correlations
between key parameters of galaxies, such as the luminosity of a
spiral galaxy and its rotation velocity: the more luminous a spiral galaxy
is, the higher its rotation velocity.
By comparing between the scaling relations of galaxies in the present-day
universe and those at earlier cosmic epochs, we can infer the evolution
of key galaxy parameters like luminosity or size with high precision.
The evolution derived from observations can then be compared to
theoretical estimates or predictions based on computer simulations, ultimately
allowing a deeper understanding of the physical processes which shaped
the "zoo" of galaxies as we observe it today.
I also am interested in supermassive black holes
(black holes which are millions or even billions of times more massive than
and the influence
they have on their host galaxies. When matter is falling into
a supermassive black hole, a large fraction of the "swallowed" mass is turned
into radiation. The central region of the host galaxy thus becomes
very luminous and turns into a so-called Active Galactic Nucleus
(abbr. AGN). For quite some time, it was assumed that AGN phases are mainly
triggered by mergers of similar-mass galaxies, termed major mergers.
However, a study I conducted as part of the
shows that this is unlikely:
we did not find a significant difference between the (quantitative)
morphologies of galaxies with an AGN and those without an AGN, which is
incompatible with the scenario of major mergers being the main AGN
Further information about my work, including links to some of my publications,
can be found in the menu under
. Note that the summaries given there
require some astrophysical background.