IMPRS projects at MPE/HEG |
The High Energy Astrophysics group at MPE has its major scientific emphasis on the study of extreme processes mostly 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.)Investigating physical processes including strong gravity around black holes and other compact objects; 4) gamma-ray bursts. Research fields for which PhD projects are offered specifically for 2016 include: |
Precision cosmology with galaxy clusters
We live in the epoch of numerous large surveys, aiming to constrain the dark energy equation of state. Many of the methods adopted by those surveys rely on using galaxy clusters to probe the evolution of large scale structure of the Universe. Currently, the use of clusters for cosmology is limited by the systematics, associated with our lack of understanding of galaxy clusters. There is an emerging need to understand how the different efforts on finding the clusters through Sunyaev-Zeldovich effect, gravitational distortion of the shapes of galaxies, concentration of red galaxies and X-ray emission are related to each other. We also would like to understand whether we can benefit from using external data to calibrate the X-ray selected clusters of galaxies. For that, the proposal is to embark on comparing the multiwavelength properties of clusters, that are selected in a different manner and to confront this to the results of numerical simulations. Supervisors: A. Finoguenov, K. Nandra |
A serendipitous Chandra galaxy cluster survey
Although XMM has two serendipitous surveys of galaxy clusters (XCLASS and XCS), there has only been one major serendipitous cluster survey (CHAMP). Surveys of galaxy clusters are important to examine cosmology, using clusters as tracers of mass, or for understanding the astrophysics of clusters. Chandra has a smaller field of view and lower sensitivity compared to XMM, but has a better ability to remove contaminating point sources. This project will be to develop automated pipelines for the detection of extended objects or clusters in Chandra observations and apply them to the Chandra archive. MPE (such as GROND) and international facilities will be used to confirm candidates as clusters. The sample will be applied to examining cosmology and cluster physics. Supervisors: J. Sanders, K. Nandra |
Analysis of metals in massive, relaxed clusters
Galaxy clusters act as reservoirs of metals ejected from stellar processes. Examining the distribution of metals in elements tells us about the stellar processes (e.g. Type Ia or Type II supernovae, or AGB stars) responsible for the enrichment. This project aims to examine the metals in a sample of relaxed luminous galaxy clusters. The aim of the project is to examine the relative role and mechanisms of enrichment by the central BCG and other galaxies. Optical and multiwavelength data will be used to link this to the stellar populations in the BCG. By examining the shape of the metallicity profile, limits on diffusion will be obtained. Supervisors: J. Sanders, K. Nandra |
The physics of the most luminous, distant AGN: accretion and feedback at the extremes
The highest luminosity quasars, at any cosmic epoch, are perhaps the most valuable jewels in the treasure chests of large astronomical surveys; such rare objects can uniquely shed light on the most extreme and violent process taking place in the nuclei of galaxies. These quasars represent short- lived phases during which the accretion process, probably operating at, or even above, the Eddington limit, deposits large amounts of energy into the surroundings. This process has been considered as a prime mover in models of galaxy formation, for its potential to strongly influence star-formation throughout the quasar’s host galaxy. The goal of the project is to study the physical properties of the most luminous, distant QSOs, both by studying in great detail their X-ray spectral properties, revealing physical characteristics of the most rapidly accreting black holes, and the multi wavelength properties of their host galaxies, to reveal the “feedback” impact of the energy released by the QSOs at the height of their accretion history. In the first phase, data from past and currently operating X-ray telescopes (ROSAT, Swift, and, in particular XMM-Newton) will be used, together with optical/NIR photometric and spectroscopic data, most of which have been already secured. In the second phase, after mid-2017, eROSITA data will be available to expand the reach of the study to larger samples, enabling robust population studies of such objects. Supervisors:A. Merloni, K. Nandra |
Testing strong gravity effects in accreting black holes
Both Active Galactic Nuclei (AGN) and Galactic Black Holes (GBH) show broad reflection Fe K lines. These lines are broadened by the movement of the material of the accretion disc and they are shaped by special and general relativistic effects, such as: Doppler shifts, gravitational red-shift, and light bending. Thus, the study of the shape and variability of broad Fe K lines provide us with an excellent tool to measure the geometry and dynamics of the matter distribution down to the last stable orbit of the accretion disc and to even constrain the BH spin. This exercise is complicated by the possible presence of ionised gas along the line of sight that can produce features mimicking the broad Fe K line shape. Therefore, in order to safely extract information on the innermost regions around the BHs through the reflected Fe K line, the impact of the absorbing material for each source has to be carefully diagnosed. This is possible with deep exposures and spectral variability studies of the brightest AGN and GBH observed with the highest effective area X-ray instruments. Supervisors:G. Ponti, K. Nandra |
Exploring the end states of massive stars by X-ray emission from neutron stars
and supernova remnants
Identified radio supernova remnants (SNRs) in the Galaxy comprise an incomplete sample of the SNR population due to various selection effects. ROSAT performed the first All-Sky Survey (RASS) with an imaging X-ray telescope and thus provided another window for finding SNRs and compact objects that may reside within them. eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian Spektrum-Roentgen-Gamma (SRG) mission which is currently scheduled for launch in spring 2016. In the soft band (0.5-2 keV), it will be about 30 times more sensitive than ROSAT, while in the hard band (2-8 keV) it will provide the first ever true imaging survey of the sky. It supports to continue the previous SNR identification campaign and to search for new supernova remnants and pulsars with a much higher sensitivity than was possible before. In the course of the PhD research the current identification campaign of SNR candidates and neutron stars shall be continued using existing multi-wavelength data from optical, radio and X-ray missions as well as from eROSITA once the mission is up. Supervisor: W. Becker |
Supernova explosions: high-energy aspects
Supernovae obtain their light from radioactive decay of 56Ni, and, in later phases of the expansion or early remnant, from radioactive decay of 44Ti. Complementing low-energy radiation, which is measured in IR to X-rays, the direct measurements of gamma-rays from radioactive decays, and from positron annihilation associated with these, gives direct insights for a few nearby supernovae. SN1987A, CasA, Tycho, Kepler, and a few candidate objects have been discussed. INTEGRAL's key program on Cas A and Tycho will add new data from 2016 on. This thesis will address the analysis and interpretation of gamma-ray data as combined with X-ray data (XMM, others) and data at lower energies. Supervisors: R. Diehl |
Massive star groups as material and energy sources
Groups of massive stars energise their surroundings through winds and supernovae, and eject material including newly formed atomic nuclei into interstellar space. These impacts and their feedback on the ISM and on subsequent star formation has been studied in our MPE group in a multi-wavelengths approach, combining high-energy data from radioactive decays with emission from hot plasma in interstellar cavities, cold gas in atomic and molecular lines, and ionisation tracers. Nearby massive star groups in the Galaxy are the objects of our studies, which also is linked to a DFG priority program project. This project will study such data variety and combine it with population synthesis work on massive star groups using latest stellar evolution models towards assessment of the outputs and feedback traces of massive star groups. This project will also exploit new data acquired by INTEGRAL for this project in 2016. Supervisors: R. Diehl |
Positrons in our Galaxy
Positrons are created by a variety of known sources such as pulsars, accreting binaries, and also sources of new atomic nuclei. Characteristic gamma-rays have been measured with INTEGRAL to reflect annihilation of such positrons. The image of this gamma-ray emission is one of the major puzzles of current high-energy astrophysics. Our group has recently achieved high-resolution spectroscopy of this emission discriminating different source regions, and also identified a microquasar and a source central in our galaxy as sources. We also had initiated a new approach to analyse such data by using information field theory. The new project will combine and deepen those pioneering works. This project will also exploit new data acquired by INTEGRAL for this project in 2016. Supervisors: R. Diehl |