Research projects

My scientific life so far concentrated on the detailed modelling of the nuclear distribution of gas and dust with various modelling approaches. During my Diploma and Phd thesis in Prof. Dr. Meisenheimer's group at the Max-Planck- Institute for Astronomy (Heidelberg, Germany), the main goal of my work was to provide models of AGN tori with the help of hydrodynamic simulations in combination with radiative transfer calculations for the direct comparison to observations, mainly with the MIDI instrument. During my ongoing postdoc position in Prof. Dr. Burkert's Physics of Galactic Nuclei group, we concentrate on the detailed micro physics happening in the direct vicinity of black holes.
On this page, a short overview over our research work is given (in inverse chronological order).
If you have any questions please do not hesitate to contact me.

The nuclear disk in the Seyfert 2 galaxy NGC 1068

We employ 3D hydrodynamical simulations with the PLUTO code. The physical scenario is the same as described below, but here we concentrate solely on the turbulent mass input from the evolving nuclear star cluster, ameliorated several routines and adapted the parameters to NGC 1068. In order to capture the relevant physics in the inner disk, which builts up, we use the mass flowing into the central region and feed it into 1D effective disk simulations, where we take viscous evolution and star formation into account. We find that the disk properties like size, mass and accretion towards the centre are in good agreement with observations. This shows that stellar evolution in nuclear star clusters is an important mechanism for obscuring and feeding black holes and triggering activity cycles.

Stellar disks in the Galactic Centre

With the help of the Gadget-2 code (Springel 2005), we investigate a scenario for the build-up of the young stellar disks in the Galactic Centre. In our mechanism, molecular clouds cross over the black hole in parts. Redistribution of angular momentum by colliding material with opposite angular momentum finally results in disk sizes and eccentricities in good comparison with observations. The best simulation of our parameter study results in an outer radius of 1 pc, a mass of 1.0e4 solar masses and an eccentricity of 0.24 for the Toomre unstable disk, which compares well with the observations. The work was mainly done by Christian Alig.
See also the paper on astro-ph!

Turbulence in AGN tori

We study the characteristics of turbulence in AGN tori, stirred by discrete energy input mechanisms like supernova explosions or stellar winds and determine the timescales of the decay of the thickness of the resulting density distribution. Below, a cut along a meridional plane is displayed after 10 orbits. This study will show us, whether long term stirring processes are needed.

From hydrodynamics to observables

With the help of the gas densities and the temperature distribution from the hydrodynamic simulations as discussed below, we determine the corresponding dust density distribution. Put into MC3D, we model spectral energy distributions and surface brightness distributions. Whereas SEDs are compared to high resolution observations, surface brightness distributions can be further processed to compare to visibility information available from interferometric observations, e.g. by MIDI in the mid-infrared regime. Shown below are images at 12 micron for the dust distribution from the above hydrodynamics run. The inclination angle changes from a face-on view to an edge-on view in equal steps. Values are given in pc.

Hydrodynamic models of AGN tori

In our hydrodynamic simulations with the help of the TRAMP code, we aim at realistically modelling gas distributions within the torus. It is made up of at least three different components: molecular gas and dust is embedded into hot gas with temperatures of typically around 10⁶K. In our hydrosimulations, this multiphase medium is produced by the interplay of discrete mass and energy input due to stellar evolution of a nuclear central star cluster and optically thin radiative gas cooling in the gravitational potential of the star cluster and a supermassive black hole. The animation on the right hand side shows the evolution of temperature of one of our simulations, during 10 obits at 5pc (the torus radius).

Clumpy 3D tori

As lots of evidence gathered for tori to be clumpy, we set up a real three-dimensional model with randomly distributed spherical clumps in an overall wedge-like shaped toroidal structure. This set of images shows visibilities plotted against position angle, when we successively increase the baseline length of the interferometer (lower left). The lower right shows deviations from the mean value. In the upper row, the UV-plane as well as the original image at 12 micron is shown, according to the corresponding aperture.

Radiative Transfer modelling of AGN tori

In a first attempt, we modelled spectral energy and surface brightness distributions by applying the analytical hydrostatic TTM-model of Prof. Dr. Max Camenzind. The main results of these axisymmetric simulations with the help of the 3D radiative transfer code MC3D have been published in Schartmann et al. 2005. Displayed in the adjacent figure is an inclination angle study for 13 micron images of our standard model, given with a linear color scale and, therefore, pronouncing the brightest areas of the image.



More images and movies of our simulational work can be found on my online material page.




Part of the work presented above was done in collaboration with various people, among them (in alphabetical order):
Christian Alig, Prof. Dr. Andreas Burkert, Prof. Dr. Max Camenzind, Prof. Dr. Thomas Henning, Michaela Hirschmann, Dr. Hubert Klahr, Dr. Martin Krause, Prof. Dr. Klaus Meisenheimer, Dr. Konrad R.W. Tristram, Dr. Sebastian Wolf.