The High Energy Astrophysics group at MPE has its major scientific emphasis on studying extreme processes primarily via X-ray observations but also extends to other wavebands. Our main astrophysical themes are 1.) Large-scale structure, as probed hot gas in clusters and groups of galaxies, and the related cosmological implications; 2.) The cosmic history of black hole growth and its relationship to galaxy evolution; 3.) The physical processes, including strong gravity, around black holes and other compact objects; 4.) High-energy transients (incl. Tidal Disruption Events and Gamma-ray Bursts.)
In addition to the generic projects offered for 2026, please consider the following:
The eROSITA-4MOST synergy: Unveiling Black Holes growth with the largest spectroscopic survey of X-ray AGN
The eROSITA X-ray All-Sky Survey has delivered the largest sample of X-ray emitting supermassive black holes across cosmic time, with millions of AGN detected in the first four passes of the survey. Starting in 2026, the 4MOST multi-object spectroscopic survey will obtain optical spectra of the majority of eROSITA detected AGN, providing a highly complete optical spectroscopic census of accreting black holes shining in X-rays, and revealing the physical connection between the growing black holes, their accretion flows and the host galaxies. The combination of eROSITA and 4MOST data, in conjunction with the its SDSS-V precursor, will allow us to constrain the physics of AGN activation, their cosmic evolution and clustering properties, and explore the connection between AGN and large-scale structure up to z~6. The PhD project will be focused on the design, execution and scientific exploitation of the most comprehensive multi-object spectroscopic surveys of active galactic nuclei to be carried out as part of the 4MOST program.
Supervisors: Dr. Andrea Merloni, Prof. Kirpal Nandra
Exploring the outskirts of clusters of galaxies with Einstein Probe
Clusters and groups of galaxies are some of the most massive objects in the universe. Most of the baryons in clusters are in a hot plasma which is visible by its X-ray emission. Using X-ray observations we can measure the thermodynamic properties of this plasma. However, the outskirts of clusters, which make up a large fraction of total cluster volume, are poorly characterised in X-rays because of their low X-ray surface brightness. These regions are very interesting scientifically, as the connect clusters to their surroundings, and are sensitive to their evolution and non-equilibrium plasma effects, such as clumping. Recently, the Einstein Probe (EP) X-ray observatory was launched. It has the combination of large field of view and low background, making it an excellent facility to observe cluster outskirts. This project is to study the outskirts of nearby clusters and groups observed using EP. By studying the X-ray emission the student will address questions such as role role of clumping and non-equilibrium effects in clusters, and study how clusters interact with their environments.
Simulated galaxy cluster (Reiprich et al 2013). The circles show radii of r_500 (an overdensity of 500 times the critical value), r_200, r_vir (the virial radius) and 3r_200, moving outwards. The inner circle is the region easily accessible to X-ray telescopes
Evolution of Supermassive Black Hole Accretion at High Redshift
Accreting supermassive black holes (SMBH) in active galactic nuclei (AGN) may play a significant role in shaping the formation and evolution of the first galaxies, and their radiative output can also be important for the reionization of the Universe. One of the best ways of finding growing SMBH is using X-ray surveys, where the contrast between the accretion power and stellar output of the galaxies is high, and because the X-rays can penetrate any surrounding obscuring gas and dust. Despite this, the number of X-ray-selected AGN currently known at high redshift is very small. The aims of this project are to search for such objects in both deep and wide X-ray surveys, identifying them with multiwaveband data from LSST and Euclid. The aim is to contrain the X-ray luminosity function at high redshifts to provide the first census of the accretion power in the Universe during this early epoch in the formation of black holes and galaxies. The project will lead naturally into the exploitation of the eROSITA all sky survey, expected to uncover numerous high redshift AGN into the epoch of reionization at redshift larger than 6.
Parametric models of the XLF extrapolated to z = 6.05 FRom Wolf et al 2021.
Cosmology with Multi-wavelength Surveys
Clusters of galaxies, located at the peaks in the cosmic density field, offer an independent and powerful probe of the growth of structure.
The properties of galaxy clusters, being sensitive to underlying cosmology, can be utilized to extract valuable information on the underlying cosmological model.
With the advent of the new eROSITA All-Sky Survey, we are on the verge of discovering more than 100,000 clusters of galaxies.
Combined with the other multi-wavelength wide-area surveys, e.g., Dark Energy Survey, eROSITA will constrain the cosmological parameters at a percent level precision at the end of its All-Sky Survey.
Complimentary to the traditional analysis methods, deep machine learning techniques provide a revolutionary way to optimally extract cosmological
parameters using the data from large-scale multi-wavelength surveys. In this Ph.D. project,
the successful candidate will learn how to analyze and process the eROSITA data of clusters of galaxies detected in the all-sky survey.
Studying the properties of these clusters will enable significant improvements in our understanding of the formation and evolution of the most massive
collapsed structures in the Universe.
