Theoretical Astrophysics Group Cologne (TAC), Germany
Postdoctoral researcher within the DFG Collaborative Research Centre Habitats Of
Massive Stars Across Cosmic Time (SFB 1601)
2021 - 2023
Theoretical Astrophysics Group Cologne (TAC), Germany
Postdoctoral researcher within the "NRW Profilprojekt Big Bang to Big Data (B3D)"
2021
Max Planck Institute for Astrophysics, Garching, Germany
Ph.D. Astronomy (Magna Cum Laude) awarded by the Ludwig Maximilian
University of Munich with Prof. Dr. Simon D.M. White, supervised by Dr. Thorsten
Naab
2017
University of Cologne, Germany
M. Sc. Physics with Prof. Dr. Stefanie Walch-Gassner
For my part I know nothing with any certainty, but the sight of the stars makes me dream.
Vincent Van Gogh
Research
The simulated multiphase interstellar medium.
I am interested in the evolution of the interstellar medium, galactic outflows, and how massive
stars shape their environment and regulate star formation with their feedback.
Within the SILCC project,
I systematically study the impact of supernovae, stellar winds, ionising UV radiation, cosmic
rays and runaway stars on star formation and the capabilities to drive and sustain galactic
outflows. Using state-of-the-art simulation techniques, particularly focusing on the role
of cosmic rays, I delve into understanding the mechanisms driving galactic outflows and
regulating star formation processes.
I mainly use the MPI parallel, magneto-hydrodynamics (MHD), 3D adaptive mesh refinement (AMR)
code FLASH to carry out my research with
high-resolution ISM simulations on high-performance computing (HPC) clusters like SuperMUC-NG.
Star formation rate surface density vs gas surface density of ISM
simulations with increasing feedback complexity.
Stratified disk simulation with an initial gas surface density of Σ = 50
M☉ / pc2. The simulation includes stellar feedback in the form of
type II supernovae, stellar winds, ionising UV radiation, and cosmic rays, as well as a type
Ia supernova background, and runaway stars. Shown are the edge-on (top row) and face-on
(bottom row) views of the total gas, ionised, atomic, and molecular hydrogen column
densities. Individual HII regions (3rd panel) from active star clusters are visible. Also
shown is the density-weighted column of the magnetic field strength (6th panel) and slices
through the centre of the simulation box with temperature (2nd panel) and CR energy density
(7th panel). The star-forming galactic ISM is concentrated around the midplane. White
circles in the 1st and 3rd panels indicate star clusters with different masses. The smallest
white circles are individual runaway OB stars. Translucent symbols indicate old star
clusters with no active massive stars in them. Stellar feedback generates a highly
structured and turbulent multiphase ISM with all its major thermal and non-thermal
components.
In addition to simulation-based research, I am actively involved in predicting and analysing the
observable properties of the ISM through post-processing and synthetic observation techniques.
Utilising sophisticated tools such as the photo-ionisation code Cloudy, I focus on studying
the
optical emission line properties of simulated ISM environments. By combining simulation data
with observational constraints, I study the underlying physical
processes governing the ISM its emission lines. Through detailed analysis of optical line
emission and line ratio diagnostics, I strive to bridge the gap between theoretical simulations
and observational data, advancing our understanding of the ISM and its role in galactic
evolution.
Emission map of the simulated ISM within the SILCC framework.
In addition to my research endeavors in ISM simulation and emission line studies, I am actively
engaged in projects that intersect with machine learning (ML) and research data management
(RDM),
particularly within the Collaborative Research Center "Habitats of Massive Stars across Cosmic
Time" (CRC1601) and the "Big Bang to Big Data" (B3D) consortium.
Within these collaborative frameworks, I contribute to initiatives aimed at integrating machine
learning techniques into astrophysical research. I am exploring new ways of ultilising machine
learning techniques for data reduction and
post-processing of the large datasets which are produced by simulations.
Furthermore, I play a role in research data management efforts within both the CRC and the B3D
project. Recognising the importance of adhering to FAIR principles (Findable, Accessible,
Interoperable, Reusable) , I am involved in developing
metadata standards for astrophysical simulation data, ensuring that research data remains
accessible and comprehensible for future generations of scientists.
Remember to look up at the stars and not down at your feet. Try to make sense of what you
see and wonder about what makes the universe exist. Be curious. And however difficult life may seem,
there is always something you can do and succeed at. It matters that you don't just give up.
We analyze SILCC-Zoom project simulations' synthetic emission maps (12CO, 13CO, [C II])
of
molecular clouds. Our zoom-in simulations track H2, CO, and C+ evolution in the
interstellar
medium with and without radiative stellar feedback. Post-processing with CLOUDY
addresses
higher carbon ionization due to stellar radiation in H II regions. Synthetic [C II]
emission
maps reveal depletion around feedback bubbles, attributed to C+ ionization into C2+. The
cloud-averaged luminosity ratio for 12CO and 13CO is unreliable for H2 mass fraction or
cloud evolutionary stage determination. Chemical equilibrium assumption introduces
intrinsic
errors in chemical abundances, luminosities, and ratios.
We introduce a FLASH code post-processing module for simulating Supernova (SN) remnants'
cooling radiation, using collisional excitation data from MAPPINGS V. Applying it to an
SNR
simulation, we find dominant EUV emissions, while optical lines ([O III], [N II], [S
II],
Hα, Hβ) are typically more observable. Our shock detection scheme reveals [S II] and [N
II]
emissions from the thin shell, and [O III], Hα, and Hβ from the hot gas within the SNR
bubble. Optical lines are influenced by the SNR's structure and projection, with 10–80%
reduction in line luminosity due to line-of-sight absorption. Contaminating background
radiation subtraction is essential for accurate SNR classification on oxygen or sulfur
BPT
diagrams. Synthetic observations match well with simulation results, but electron
temperature and density sensitivity to assumed metallicity is noted.
We present MHD simulations of the star-forming interstellar medium in stratified
galactic
patches (Σgas = 10, 30, 50, 100 M⊙ / pc^2). The SILCC project includes non-equilibrium
thermal
and
chemical processes. The sink-based model incorporates stellar winds, UV radiation,
core-collapse
supernovae, and cosmic rays (CR). Simulations align with the observed Σgas-ΣSFR
relation.
CRs
impact outflows; without them, a two-phase to single-phase transition occurs. With CRs,
three
phases persist, dominated by the warm phase. CR impact on mass loading decreases with
higher
Σgas, maintaining factors around unity, independent of ΣSFR. Vertical velocity
dispersions
of
the warm ionized medium (WIM) and cold neutral medium (CNM) correlate with ΣSFR^0.20,
consistent
with observations. In the absence of stellar feedback, no correlation is observed. WIM's
velocity dispersion is ~2.2 times higher than CNM, matching local observations.
If you want to build a ship, do not drum up the men to gather wood, divide the work, and
give orders. Instead, teach them to yearn for the vast and endless sea.
So when I look up at the night sky and I know that, yes, we are part of this Universe, we
are in this Universe, but perhaps more important than both of those facts is that the Universe is in
us. When I reflect on that fact, I look up, many people feel small - 'cause they're small and the
Universe is big - but I feel big because my atoms came from those stars.
Neil deGrasse Tyson
Contact
Dr. Tim-Eric Rathjen
University of Cologne
Institute for Astrophysics
Zülpicher Straße 77
50937 Cologne
Germany
When I heard the learn’d astronomer, When the proofs, the figures, were ranged in columns
before me, When I was shown the charts and diagrams, to add, divide, and measure them, When I
sitting heard the astronomer where he lectured with much applause in the lecture-room, How soon
unaccountable I became tired and sick, Till rising and gliding out I wander’d off by myself, In the
mystical moist night-air, and from time to time, Look’d up in perfect silence at the stars
