Das Radioteleskop an der Universitäts-Sternwarte dient im Astro-Master-Praktikum zur Messung der Rotation der Milchstrasse aus der Dopplerverschiebung der 21cm Wasserstoff-Linie. Durch die neue Teleskophalterung soll die Zielausrichtung auf 0.1 Grad erhöht werden und HI-Wolken reproduzierbar wiedergefunden werden. Für eine grosse Anzahl von Messungeng soll getestet werden, ob durch Dekonvolution einer Gaussschen Verbreiterung die Auflösung erhöht werden kann. Gute Python-Kenntnisse sind wünschenswert.

With the upcoming Square Kilometre Array (SKA) and its precursor telescopes, radio astronomy is undergoing a renaissance. New algorithms, data reduction methods and survey modes are actively developed to handle the EB-scale raw data streams produced and to utilise the full potential of these new instruments. As part of a large collaboration, our group at LMU is developing commensal line intensity mapping and interferometric imaging using scanning observations. Such interferometric scanning or on-the-fly (OTF) observations are increasing the survey speed by removing the settle-and-slew overhead while also enabling commensal single-dish intensity mapping, providing a dramatic improvement in data acquisition efficiency. However, the scanning motion of the antennae pointing relative to the delay centre introduces smearing effects that need to be corrected in the imaging process. In particular, the smearing of the primary beam (PB) response introduces flux-density errors in the interferometric images. This project aims to model the smeared PB by measuring the flux-density variation of thousands of sources detected in our pilot MeerKAT OTF observations. The developed PB models and software will be incorporated into our OTF imaging pipeline, which we will use to reduce 100+ hours of MeerKAT OTF data observed in the upcoming year by our collaboration.

In Rahmen von laufenden Forschungsprojekten können bestimmte Teilaspekte bearbeitet werden, z. B. die Korrelation von Objektlisten in verschiedenen Wellenlängenbereichen (vom Röntgenlicht bis hin zum sub-mm-Bereich).

Die Modellierung von dreidimensionalen Galaxien wird oft mit der Schwarzschild-Methode durchgeführt. Man rechnet Sternbahnen in einem gegebenen Gravitationspotential und findet die optimale Mischung, die die gemessenen Daten am besten reproduzieren kann. Die Modellierung von Galaxien mit Scheiben, die fast zweidimensional sind, mit derselben Methode stellt Fragen, die noch ungelöst sind. Wie optimiert man die Berechnung des Potentials? Wie bestimmt man die richtige Regularisierung (d. h. die Glättung) der Lösung? Wie gut ist die Methode für realistische Galaxien? Während der Arbeit werden Lösungen zu diesen Fragen getestet und implementiert.

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:

1. 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.

2. 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.

The observed bimodal distribution of local Universe galaxies in star formation properties (from optical color-magnitude and stellar mass-star formation rate diagrams) is due to the process of star formation quenching, making once star forming spiral galaxies to non/little star forming elliptical/S0 galaxies. There are many possible processes responsible for this observed star formation quenching, among which ram-pressure stripping is the dominant mechanism in dense galaxy cluster environment. The hot (10⁷ . . . 10⁸ K) and dense (n_e ~ 10⁻⁴ . . . 10⁻² cm⁻³) intracluster medium can strip cold gas from the spiral galaxy disk, which eventually truncates star formation as the galaxy moves though the cluster environment. We have acquired ultraviolet data for a sample of galaxies undergoing ram-pressure stripping (with tentacles of star formation along the stripped tails with the galaxy disk resembling a jellyfish) where the ongoing truncation of star formation can be directly studied comparing with emission line diagnostic maps made from MUSE IFU data. This project involves studying the star formation progression in a galaxy undergoing ram-pressure stripping with indications of truncation along the galaxy disk. There are opportunities to collaborate with a larger team involved in multiwavelength analysis of jellyfish galaxies.

Der dominante Anteil von Galaxien in Galaxienhaufen sind “rote” Galaxien (S0 oder elliptische Galaxien), d. h. Galaxien ohne gegenwärtige Sternentstehung. Das führt dazu, dass sie sich im Farben-Magnituden-Raum auf der sogenannte “red sequence” befinden. In Multi-Band photometrischen Surveys (z. B. dem Dark Energy Survey DES) findet man Galaxienhaufen durch ihre red-sequence-Galaxienpopulation, und bestimmt ihre (photometrischen) Rotverschiebungen an Hand der Farben der red-sequence-Galaxien. Die Anzahl der roten Galaxien eines Galaxienhaufens wird benutzt um seine “Richness” festzulegen, eine Zahl, die stark mit der Gesamtmasse des Galaxienhaufens korreliert. Für viele Zwecke in der Kosmologie möchte man die in den Beobachtungen identifizierten Galaxienhaufen mit Galaxienhaufen, die numerisch im Kontext von Strukturbildung simuliert worden sind, vergleichen. Z. B. möchte man den genauen Zusammenhang zwischen Richness und Galaxienhaufenmasse und die zugehörige Streung wissen, oder man möchte wissen, wieviel dunkle Materie mit den einzelnen roten Galaxien assoziert ist (als Funktion ihrer Helligkeit und Position im Galaxienhaufen). Das Ziel dieser Masterarbeit ist es, die Technik der Beobachter, Galaxienhaufen zu finden, auf simulierte Galaxienhaufen anwendbar zu machen, und Haufenkataloge mit Richness, roten Haufenmitgliedern und dunkle-Materie-Halo-Massen der individuellen Haufenmitglieder abzuleiten. Die Ergebnisse können dann mit den Ergebnissen aus den Beobachtungen verglichen werden, und es können die Ergebnisse von gegenwärtigen und zukünftigen Beobachtungen vorhergesagt werden.

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.

• Bachelor- und Masterarbeitsthemen

• Masterarbeiten der Physical Cosmology Research Group

Gamma-ray observations allow us to study the most extreme cosmic sources in the Universe. These violent environments, which are not reproducible at Earth-based laboratories, provide opportunities to study processes at the frontier of known physics. Our group tackles a wide range of questions related to astrophysics and fundamental physics, such as probing cosmic-ray acceleration processes and the search for the nature of Dark Matter.

Over 15 years of operations, Fermi-LAT is the preeminent instrument for studying the high-energy universe in the MeV to GeV energy range. It provides a rich data set ripe for discovery of new sources and science. MAGIC is one of the current generation Imaging Atmospheric Telescopes with high sensitivity for extended sources in the Galactic Plane. The prototype of Large Size Telescope (LST) for the Cerenkov Telescope Array (CTA) has completed construction and has started partial scientific operations. Over the next four years, three additional LSTs will be built, providing unprecedented sensitivity to the gamma-ray universe. The combination of three datasets allows for highest sensitivity in studying the extreme environments within our Galaxy.

We seek Master’s students to perform their thesis work with the primary focus on the analysis of Fermi-LAT, MAGIC, and/or LST-1 data on Galactic sources such as Supernova Remnants and Galactic PeVatrons. Although not required, experience in Python and C++ is highly desired.