Jobs and Thesis
Bachelor and Master Thesis
Below we list ideas for Bachelor and Master thesis. Please also view the Doctoral Thesis topics we offer, most of which can also be scaled to Master thesis topics. We will be happy to explain in more detail and define a project that suits your interests and technical background. You could also work on any of these projects within an internship, to get to know us and the subject.
Galaxy cluster velocities from kSZ: we will use the available Planck data for some well-known clusters and see what can be inferred on their cosmic velocities, under various assumptions on mass, temperature, dust content, etc
Density inhomogeneity in galaxy clusters: we will use available SZ maps of two very well-known clusters (Coma and A2163) and combined the results with hard X-ray data from the NuSTAR satellite, to make a measurement of gas clumping using a completely new method!
Mapping of a giant radio halo: we can choose one of the known clusters from our (tons of!) VLA data and use the existing VLA pipeline to try to make a radio halo map.
ALMA SZ image of a cluster: we will combine a large amount of ALMA Compact Array data for the El Gordo cluster (over 40h) and make a map, to see if there is any hint of a shock or other structures. We shall then do some model fitting in the uv-plane.
Lensed CIB profile for a cluster: we will use a simple lensing model for a cluster for analytically predict how the flux amplification profile will look like from lensing the Cosmic Infrared Background (CIB).
Determination of Hubble constant from joint SZ and X-ray modelling: We have initiated a project to utilize state-of-the-art X-ray data from the eROSITA satellite, and SZ data from the SPTPol telescope (and in the future from Simons Observatory), to model the value of Hubble constant with these two measurements. We look forward to implement several novel techniques for this task using these current and upcoming data.
Separation of kinematic SZ and CMB-lensing with machine learning: Machine learning is a vast and rapidly growing tool in astronomical data analysis. In this project we aim to train a Convoluted Neural Network on simulated data of galaxy clusters, where the kinematic SZ and CMB-lensing signals are on top of each other, and explore how one can separate them while having only a handful of objects.
Hydrogen Recombination Lines (H-RL):This project would pick up our long-term effort to harvest the ALMA archive for observations of mm-wavelength hydrogen recombination lines (H-RL). The aim is to determine the line fluxes and relate that to the infrared-flux, in order to establish H-RLs as reliable tracers of the massive star formation rate. We have a unique software package that supports this. A related issue to follow up on is the reliability of mid-infrared imaging photometry as a proxy for the star formation rate.
High-redshift galaxy survey: In preparation for the FYST/CCAT-prime first year deep photometric high-redshift galaxy survey we want to develop innovative methods for source identification and source population analysis. Specifically, we will explore three novel approaches that can be explored in several Bachelor or Master theses. (i) Adapt and refine developments to exploit Herschel observations (Shirley et al., MNRAS 507, 129, 2021) through a Bayesian cross-matching analysis with informed priors, e.g., source position, redshift, and galaxy type from optical to IR identifications. (ii) A cross-matching analysis based on machine learning methods (An et al. 2019), trained on deep optical, Herschel, SCUBA-2 and ALMA observations of the COSMOS and GOODS fields. (iii) A holistic Bayesian fit to a parametric model describing the source ensemble properties, including redshift-dependent luminosity functions, SEDs, and biasing. We will test these analysis methods on simulated sub-mm imaging that includes all instrumental and sky noise terms. Such analysis will also inform on the best observing strategy, e. g. to balance map width vs. depth, and on the required relative depth in the observed photometric bands.
LEGO VLBI: To illustrate the principle of radio interferometry we built a model of the ALMA interferometer from LEGO pieces. The telescope configuration can be modified and the uv-coverage is updates instantly to show the resulting image of a given target. We plan to build a similar LEGO model to illustrate VLBI, with a 1-meter large globe on which telescopes can be mounted. A possible thesis would involve to modify the necessary software and design model targets, such as black holes.
Doctoral Thesis
We offer a number of PhD thesis topics as describe below. Funding for doctoral students is limit and may not be available at all times. If you are interested, please talk to Frank Bertoldi and / or Kaustuv Basu.
A next-generation galaxy cluster survey with the FYST telescope
Data from wide-area galaxy cluster surveys are one of the main drivers behind the current “golden era” of cosmology. Among the handful of methods that can reliably detect galaxy clusters and infer their masses, the Sunyaev-Zel’dovich, or SZ, effect is a unique one: its signal is practically undiminished by redshift and at frequencies below 220 GHz galaxy clusters produce a negative signal in the microwave sky. At the University of Bonn we are part of a team preparing for a new-generation SZ cluster survey with the FYST / CCAT-prime telescope, that will not only improve the raw detection sensitivity of the SZ signal compared to current generation instruments, but will also extend the measurement of the SZ effect in the sub-millimeter domain. Here the SZ signal is positive and gets mixed with contaminating foreground sources. The challenge of this thesis work will be to optimize some of the existing cluster detection methods, and develop new ones, that will yield unbiased cluster SZ measurements in the sub-millimeter wavebands for applications in cosmology and astrophysics.
Literature: “CCAT-Prime: science with an ultra-widefield submillimeter bservatory on Cerro Chajnantor”, G. Stacey et al. 2018, SPIE proceedings, arXiv:1807.04354; “Planck’s view on the spectrum of the Sunyaev-Zeldovich effect”, J. Erler et al. 2018, MNRAS, arXiv:1709.01187, CCAT-prime Collaboration: Science Goals and Forecasts wit Prime-Cam on the Fred Young Submillimeter Telescope.
Measuring the cosmic velocity field with galaxy clusters
Studying the number count of galaxy clusters is currently one of the leading methods for cosmological studies, particularly for finding out the nature of dark energy. These cluster surveys are primarily conducted in the optical, X-ray, or millimeter wavebands, where the last option make use of the so-called Sunyaev-Zel’dovich (SZ) effect for detecting and characterizing galaxy clusters out to very high redshifts. But the SZ effect measurements also provide additional benefits like inferring the proper motion of galaxy clusters (sometimes called the peculiar velocity) in the comoving cosmological frame. Measuring this velocity field will be a new and much fruitful method for constraining cosmology and particularly the dark energy models. This research project will focus on improving the cluster velocity measurement techniques based on multi-frequency SZ survey data, both from the currently available Planck satellite and also from the upcoming CCAT-prime telescope. Our group at the Bonn University is strongly involved in the latter project whose data will become available from 2021 on.
Literature: “CCAT-Prime: science with an ultra-widefield submillimeter observatory on Cerro Chajnantor”, G. Stacey et al. 2018, SPIE proceedings, arXiv:1807.04354; “Planck’s view on the spectrum of the Sunyaev-Zeldovich effect”, J. Erler et al. 2018, MNRAS, arXiv:1709.01187
Resolved SZE observations of galaxy clusters
This PhD project will prepare and conduct sensitive, high-resolution interferometric (CARMA, ALMA) and single dish (GBT, IRAM 30m, CCAT) multi-band imaging of galaxy clusters in the Sunyaev-Zel’dovich Effect (SZE). We expect to benefit in particular from using representative subsamples of eROSITA-detected clusters.
Galaxy clusters can be used as powerful probes to constrain cosmological models. They also represent laboratories to study the baryonic physics and its interplay with structure formation. Especially when observed at X-ray or millimeter/sub-mm (SZE) wavelengths, the hot, diffuse intracluster medium (ICM) allows to infer valuable information on the total mass, dynamical structure and evolutionary status of the cluster, as well as on the thermal and chemical properties of the ICM itself. Resolved SZE imaging of galaxy clusters provides important constraints on the cluster baryonicstate, revealing merger shock fronts or extended regions of shock-heated gas at any temperature. The internal bulk motions induced by mergers contribute to the kinetic SZ signal that can be detected through multi-frequency SZE observation. ALMA and single dish SZE imaging (CCAT, IRAM 30m, GBT) together can resolve all relevant scales of galaxy clusters at all redshifts, delivering accurate estimates of the integrated Comptonization parameter (used as cluster mass proxy) for samples large enough to be of cosmological significance. This project will therefore also support our efforts within the European ALMA regional center (ARC) to investigate methods and develop software for a optimal combination of ALMA interferometer and single dish imaging data.
The Mystery of Galaxy Cluster Radio Halo
Giant radio halos inside galaxy clusters are Mpc scale diffuse synchrotron emissions whose formation processes are still poorly understood. These radio halos are associated with galaxy cluster collisions, but we do not know how many of these objects are in the sky or what impact they may have on our understanding of other cluster properties. We have initiated a project to correlate cluster radio halo measurements with X-ray and SZ effect data to understand the powering mechanism and mass dependence of radio halos, as well as determining their true abundance in the sky. New data from several radio telescopes (EVLA, GMRT) have been collected and being analyzed. The goal of this PhD project will be to take a leading position in this work and measure the radio halo properties in several new clusters using this state-of-the-art radio data, aiming towards a comprehensive picture of radio halo origin.
Literature: "A Sunyaev-Zel'dovich take on cluster radio haloes -- I. Global scaling and bi-modality using Planck data", K. Basu; "A comparative study of radio halo occurrence in SZ and X-ray selected galaxy cluster samples", M. Sommer & K. Basu