deutsche Version
Master’s thesis projects
at the University Observatory
1. Instrumentation and observational projects
Diese Masterarbeit setzt Interesse an elektronischen Steuerungen und
Sensorik voraus. Vorkenntnisse in Elektronik (u. U. entsprechende
Master- oder Bachelorvorlesungen) und SPS-Technologien im besonderen
sind von Vorteil. Im Rahmen des Baus des MICADO-Instruments
für das 39-m-EELT-Teleskop in Chile sind diverse Mechanismen
und elektronische Steuerungskomponenten zu entwickeln, bauen und zu
testen. Mechanismen und Sensorik müssen in einem Test-Kroystat
(~80 K) an der USM getestet und von Beckhoff-SPS gesteuert
werden. Die Arbeit umfasst die Konzipierung, Durchführung und
Dokumentation von Tests diverser Hardware bei Raumtemperatur und bei
~80 K in unserem Kryostaten. Ergebnisse müssen aufbereitet
werden um im Rahmen des MICADO-Projekts von anderen internationalen
Konsortiumspartnern verwendet zu werden. Als Steuerungselektronik
werden Beckhoff-SPS eingesetzt. Zusätzlich kann je nach
genauem Thema ein rein astrophysikalisches Beobachtungs-
und/oder Datenauswertungsprojekt in Zusammenarbeit mit dem
Wendelstein-Observatorium absolviert werden.
2. Stars and planets
Project 2.1:
Multi-wavelength observations of star formation regions
(T. Preibisch preibisch@usm.lmu.de)
Students can carry out investigations as part of an ongoing project,
e.g., correlation of object lists in different wavelengths ranges
(from X-ray to the sub-mm regime).
The model atmosphere code developed by our working group,
“Fastwind”, is one of the world’s most used codes
to synthesize the optical and IR spectra of massive stars of spectral
types O and B.
In recent years, a comprehensive revision of this code has been
performed, which among other features also allows to model the
ultraviolet range.
This new program version, however, has not yet been adapted to
calculate the IR range of the spectrum, where just this range is of
highest relevance for new and future large telescopes (JWST, ELT).
The aim of the suggested Master’s thesis project is, in a first
step, to adapt the new “Fastwind” version so that the IR
range can be satisfactorily synthesized, including careful tests.
A comparison with results from the former program version is mandatory.
In a second step, our atomic database shall be extended so that
high precision IR spectroscopy of elements different from H and He
becomes possible.
The work suggested here requires a strong interest in working with
and implementing of numerical algorithms.
Project 2.3:
Model atmospheres and synthetic spectra for Wolf-Rayet stars
(J. Puls uh101aw@usm.lmu.de)
The model atmosphere code “Fastwind”, developed by
our group, is one of the world’s most widely used codes for
calculating the optical/IR spectra from massive stars of spectral
type O and B. The project presented here aims at stepwise extending
the code so that the spectra of so-called Wolf-Rayet stars can be
synthesized. The main difference of the atmospheres of these Wolf-Rayet
(WR) stars in comparison to those of “normal” stars is
a significantly higher wind density (practically all optical lines
are formed mainly in the wind) and a different chemical composition:
in most cases, the helium and nitrogen abundances (products of the
CNO cycle) are greatly increased, whilst the hydrogen abundance is
dramatically reduced (until zero). The work presented here requires
a strong interest in the implementation of numerical methods.
Pulsating variable stars are known to follow a relation between the
duration of the pulsation, the period, and their mean luminosity.
These so-called period-luminosity relations are one of the central
tools to get reliable distances of nearby galaxies.
Based on theoretical and observational arguments, there has been a
long discussion if these relations depends on galactic properties like,
e.g., the metallicity of the parent generation of the pulsating stars.
Long-period variable stars have, compared with short-period variable
stars like Cepheids or RR-Lyrae, been studied only sparsely.
Only in the last years a period-luminosity relation was published
based on the OGLE data, for the Magellanic clouds (which are very
close by and metal poor).
The goal of this Master’s thesis project would be to check
the long-period variable stars found in the Pandromeda survey of the
metal-rich M31 galaxy, and to build using photometry obtained from
publicly available data the period-luminosity relation for these stars.
Finally these results should be compared with the published results
for the Magellanic clouds.
3. Galaxies and AGN
Three-dimensional galaxies are often modeled using the Schwarzschild
approach.
One computes stellar orbits in a given gravitational potential and
superposes them to reproduce the available dataset.
The modeling of two-dimensional objects like galaxies with stellar
disks poses some yet unsolved questions.
How well can one compute the gravitational potential using spherical
harmonics?
What is the optimal amount of regularization?
How well can one describe real galaxies?
During the thesis project answers to these questions will be tested
and implemented.
Giant elliptical galaxies are embedded in massive dark matter halos.
Not much is known, however, about the dark matter halos of dwarf
ellipticals, because their low velocity kinematics are difficult
to measure.
Thanks to our new high-resolution two-dimensional spectrograph VIRUS-W
we were able to obtain high quality spectra for a number of dwarf
ellipticals in the Virgo cluster.
Goal of the Master’s thesis project is the reduction and analysis
of these data, their dynamical modeling and the determination of the
dark matter density in these objects.
Astronomers noticed more than 100 years ago that the galaxy
populations within dense galaxy clusters are different from those
in the surrounding low-density field, but the underlying reasons
remain unclear.
Hierarchical structure formation leads dense clusters to form rather
late in the Universe and to continue the accretion of surrounding
material, including star forming spiral galaxies where through a
range of processes they are transformed into ellipticals or S0s.
Studies over the past decades have clarified the range of physical
processes that are likely contributing to this transformation, and
these include ram pressure stripping, mean field tidal stripping and
galaxy merging, among others.
We are using a new Sunyaev-Zel’dovich effect selected
sample of galaxy clusters from SPT that extends to redshift
z ~ 2 together with data from the DES, Spitzer, and
Herschel to study these galaxy population transitions as a function
of cosmic time.
The goal of this project is to use the multi-band optical and
IR photometry to identify cluster galaxies and study the transition
in color and star formation rates as a function of radius from the
cluster center as well as a function of cosmic time and cluster mass.
Our dataset is uniquely suited for this study, because we have a well
understood sample of clusters extending over a broad redshift range
and a uniform photometric imaging dataset in the optical and IR over
large areas of the sky.
Among the many facets under investigation of the galaxy formation
and evolution puzzle, two old and still unanswered questions remain
at the core of our incomplete picture:
- How do galaxies grow their stellar mass over cosmic time?
Answering this question has proven difficult mainly because of the
uncertainties in estimating the on-going star formation for large,
representative galaxy samples.
The easily accessible ultra-violet (UV) restframe emission, in
principle a direct probe of the young short-lived massive stellar
populations, is in fact measuring only the small fraction of that
emission that has not been absorbed by the interstellar dust.
It thus needs to be corrected by factors that, depending on the
intrinsic galaxy properties, can vary by orders of magnitude.
- Why does star formation cease at a certain point during the
galaxy life?
In the last decade many studies have agreed in assigning a relevant
role to nuclear activity (AGNs, due to massive black hole growth)
in affecting the galaxy star formation histories (SFHs).
In particular, once a major burst of star formation has eventually
exhausted the gas inside the galaxy immediately available for star
formation, the so-called “radio-mode feedback” is often
invoked as preventing the gas in the outer galaxy halo from cooling
and starting star formation again.
Deep radio surveys, conducted in association with multi-wavelength
observations, allow us to probe at the same time dust-unbiased star
formation and nuclear activity, and hence have become a fundamental
tool in the last decade for studying galaxy evolution.
This master project will focus on already available JVLA radio
continuum data in the deepest extra galactic fields in order to
obtain a dust-unbiased view of star formation over cosmic time
and a first-order estimate of radio-AGN feedback to be compared
to theoretical model expectations at different redshifts and halo
masses.
Projects in the OPINAS Group (Ralf Bender et al.)
4. Cosmology, large-scale structure, and gravitational lensing
The majority of galaxies in clusters are “red” galaxies (S0
or elliptical galaxies), i.e., galaxies with no ongoing star formation.
This makes them form a “red sequence” in color-magnitude
space.
In multi-band photometric surveys (e.g., the Dark Energy Survey DES)
one sucessfully identifies clusters of galaxies by their red-sequence
galaxy population, and estimates the (photometric) redshifts for
clusters using the colors of their red galaxies.
The number of red galaxies of each cluster is used to define its
“richness” (a quantity strongly related to the total mass
of the cluster).
For many purposes in cosmology one would like to relate the
observationally identified “red sequence clusters” to
clusters numerically simulated within the framework of structure
formation.
For example, one would like to know how cluster mass and cluster
richness scales, what the scatter is, and how much dark matter
is associated with individual red galaxies (as a function of the
luminosity and position within the cluster).
The goal of this project is to apply the observers’
cluster-finding technique to simulated clusters and to derive a
catalog with cluster richness, their red-sequence member galaxies,
and dark matter halo masses of individual member galaxies.
These findings can then be compared to results from observations or
can be used to predict the outcome of ongoing and future observations.
By their (dark and luminous) matter components clusters of galaxies
distort light bundles traversing them.
This so called weak gravitational lensing effect alters the shapes
of background galaxies and aligns their major axes preferentially
tangentially to the foreground clusters centers.
One can invert the relevant relations to derive mass maps for galaxy
clusters, to measure their projected profiles and “total”
masses.
We offer projects on this topic, where either data from our own
Wendelstein 2-m telescope are taken or where public data, or data from
the Dark Energy Survey DES, are used.
Towards centers of clusters of galaxies the projected matter
density can become large enough that objects in the background of
such clusters of galaxies are mapped into multiple images and giant
gravitational arcs.
The analysis of this so-called strong gravitational lens effect yields
the most precise astrophysical mass measurements at cosmological
distances.
In addition one can constrain the amount of dark matter (i.e., the
size of dark matter halos) associated with galaxy cluster members.
In this way one can measure the cluster subhalo mass function and
the amount of dark matter stripped when galaxies fall into clusters
and pass their high density cores.
The evolution of the cosmic density field encodes powerful information
on the laws of gravity as well as the initial conditions of the
universe.
So far, most experiments that quantify the large-scale structure of
the universe only measured 2-point statistics of the density field.
This means that they measured the amplitude of density fluctuations
as a function of scale.
This provides only a limited view of the large-scale structure and
hence limited cosmological information.
Within the Dark Energy Survey (DES) Collaboration we established a
new method of analyzing the large-scale structure of the universe:
Density Split Statistics (DSS).
This method closes a major gap in current studies of the large-scale
structure:
it can disentangle gravitational non-linearities from non-trivial
features in the relation between galaxies and matter!
The reason for this is that DSS is sensitive to the skewness of
density fluctuations (as opposed to only the amplitude).
We are looking for a Master student with excellent mathematical skills
to complement our work on density split statistics.
This student will first familiarize herself/himself with our
publications Friedrich & Gruen et al. (arXiv:1710.05162)
and Gruen & Friedrich et al. (arXiv:1710.05045).
These describe density splits of the gravitational lensing power
spectrum.
The student will then transfer our formalism to also incorporate
density splits of the galaxy power spectrum.
One of the leading methods for studying the cosmic acceleration,
measuring neutrino masses and directly measuring the growth rate
of cosmic structures is through studies of the redshift and mass
distribution of uniformly selected samples of galaxy clusters.
A key element of these studies is constraining the masses of the
galaxy clusters using information from weak gravitational lensing.
The goal of this project is to use the available weak gravitational
lensing mass information from the Dark Energy Survey within
samples of galaxy clusters selected from the South Pole Telescope
Sunyaev-Zel’dovich effect survey or the RASS (and soon from eROSITA!)
X-ray survey to study the cosmic acceleration, neutrino masses, and
the growth rate of cosmic structures.
- Understand the impact of surrounding large-scale structure and
miscentering on the weak-lensing mass estimates of galaxy clusters.
Application to real cluster sample with DES shear catalogs to
constrain masses.
- Understand the impact of contaminating impacts due to X-ray
and radio AGN on the selection and cosmological analysis of galaxy
cluster samples.
- Measure correlations among cluster observables in the X-ray,
SZE, and optical and study their impact on cosmological analyses.
Projects in the Physical Cosmology and OPINAS Groups (Jochen Weller et al., Ralf Bender et al.)
5. Computational and theoretical astrophysics
Research in the Computational Astrophysics Group (CAST) ranges from
the theoretical investigation of star and planet formation to studies
of processes on cosmological scales.
A variety of different, well-known numerical codes (such as Ramses,
Gadget, Sauron, Gandalf, Mocassin, and others) are used.
Primary investigations regard the formation, the structure, and
the evolution of protoplanetary disks, the formation of planetary
building blocks and planets, the relation between turbulence and phase
transitions in the multiphase interstellar medium (ISM), energetic
feedback processes, molecular cloud and star formation in galaxies, as
well as cosmological structure and galaxy formation and the interplay
between feedback processes, AGN, and galaxy evolution and their imprint
on the intergalactic medium (IGM) or the intercluster medium (ICM).
Thus, our group studies astrophysical processes on length scales
covering more than 14 orders of magnitude, from gigaparsec scales
of cosmological structures all the way down to sub-AU scales of dust
grains within protoplanetary disks.
It is now clear that small-scale processes like the condensation
of molecular clouds into stars, magnetic fields and the details of
heat transport as well as large-scale processes like gas infall from
the cosmic web into galaxies and environment are intimately coupled
and have to be investigated in a concerted effort.
The various past and ongoing projects within the CAST group cover
a link between the various scales and contribute to our understanding
of crucial aspects of the formation and evolution of stars and
protoplanetary disks, central black holes and AGNs, star-forming
regions and the ISM, galaxies and their IGM, galaxy clusters and the
ICM as well the large-scale structures in the universe.
They also also drive the continuous effort to develop and to apply
new numerical methods and the next generation of multi-scale codes
within the framework of numerical astrophysics.
Past and ongoing Bachelor’s and Master’s thesis projects
were always offered with respect to the individual strengths and
interests of the students and cover various areas in the field of
computational and theoretical astrophysics:
- Formation of large-scale cosmological structures (dark-matter
halos, galaxies, clusters of galaxies, role of black holes, magnetic
fields and non-thermal particles)
- Evolution and structure of the turbulent interstellar medium
(ISM physics, self-regulating star formation, formation of molecular
clouds, magnetic fields)
- Physics of galactic centers (active galactic nuclei, origin and
nature of the gas cloud G2 near the Galactic center)
- Formation of planets, stars, and stellar clusters (stars and
their influence on the surrounding protoplanetary disc, interstellar
matter, radiative transfer, dynamics of particles and planets in
protoplanetary disks)
- Application and development of numerical tools on parallel
CPUs and GPUs and visualization (particle-based
SPH/N-body, grid-based,
moving-mesh or meshless methods)
More detailed information on
ongoing and finished projects
as well as more detailed information on ongoing research can be
found on the web pages of the
Computational Astrophysics Group.
|
