PhD Projects

//PhD Projects
PhD Projects 2021-09-17T09:29:12+00:00

Fundamental Physics in Radio Astronomy Group at the MPIfR

Director: Prof. M. Kramer

Group website

The Fundamental Physics in Radio Astronomy group of the MPIfR led by Prof. Michael Kramer concentrates on various aspects of fundamental physics, namely the Galactic population of neutron stars, their use for precision tests of general relativity and alternative theories of gravity, the detection of low-frequency gravitational waves and the structure and properties of super-dense matter. To do this we use the largest radio telescopes around the world, including our own 100-m telescope in Effelsberg, the MeerKAT array in South Africa and FAST in China.

We are seeking a student for one of the following research areas:

a) Searching for pulsars and transient radio sources 

The discovery of new pulsars frequently leads to new scientific results depending on the pulsar’s properties. With recent advancements in receivers and computing we are able to probe deeper into the Galaxy than ever before. Radio astronomy also offers a unique chance to explore the dynamic sky as many energetic processes are expected to be visible in this part of the electromagnetic spectrum.

b) Pulsars as probes of gravity 

Pulsars are very compact objects, exhibiting the strongest gravitational fields next to black holes. Acting as cosmic lighthouses and precise cosmic clocks, pulsars can be used to probe gravitational physics under strong-field conditions. High precision timing of pulsars provided the first, evidence for the existence of gravitational waves as predicted by Einstein’s theory of gravity (Nobel Prize 1993), and leads to some of the best constraints on alternative gravity theories. Our research in that field of experimental gravity is driven by improvements in instrumentation, new pulsar discoveries, and ongoing theoretical work.

c) Pulsar as detectors for low frequency gravitational waves 

The direct detection of gravitational waves from merging black holes with LIGO has opened up a completely new window to the Universe: the gravitational wave sky. Using a Pulsar Timing Array a number of high-precision millisecond pulsars are timed to detect low frequency gravitational waves,  and complement the observations of ground-based gravitational wave detectors like LIGO and VIRGO. To make such a detection a European collaboration, the European Pulsar Timing Array, uses the largest radio telescopes in Europe, including the 100-m radio telescope in Effelsberg.

d) Pulsars as probes of super-dense matter and stellar evolution 

Neutron stars represent the most extreme state of matter in the observable Universe. We can study the properties of this super-dense matter when we observe neutron stars in the form of radio pulsars, e.g. mass measurements in binary pulsars offer some of the best constraints for the “equation-of-state”. These mass measurements also offer clues for understanding the birth mass distribution of neutron stars and for the evolution of different types of binary pulsars.

The applicant’s research proposal should be related to the above research themes.

Contact: Prof. Dr. Michael Kramer (mkramer@mpifr.de), Dr. David Champion (champion@mpifr-bonn.mpg.de), Dr. Paulo Freire (pfreire@mpifr-bonn.mpg.de), Dr. Norbert Wex (wex@mpifr-bonn.mpg.de),

Site: Bonn, Max-Planck-Institut für Radioastronomie, Fundamental Physics in Radio Astronomy Group

Fast radio bursts (FRBs) are extragalactic, short-duration radio transients with an unknown origin. In recent years evidence has been mounting for a connection between magnetars, highly magnetized neutron stars, and repeating FRBs. The focus of this project is to further explore the observational connection between radio bursts from magnetars and repeating FRBs. The student will conduct new observations with world-class observatories such as the Effelsberg 100-m radio telescope, gain experience working with large data sets, and investigate the sources’ statistical properties.

Contact:
Dr. Laura Spitler (lspitler@mpifr.de)
Prof. Dr. Michael Kramer (mkramer@mpifr.de)

Site: MPIfR, Bonn

Very Long Baseline Interferometry and Radio Astronomy Group at the MPIfR

Director: Prof. Dr. J. Anton Zensus

Group website

Very-long-baseline interferometry (VLBI) is the only method for a direct imaging of  regions in the immediate vicinity of  super-massive cosmic black holes. This includes the shadow around a black hole and its surrounding photon ring (event horizon), and thus tests Einstein’s Theory of General Relativity.

Since the angular resolution of an interferometer increases with decreasing wavelength and with increasing baseline length, millimetre VLBI and space VLBI provide the highest angular resolutions in astronomy (lower than 30 microarcseconds). Since compact radio sources become more transparent with increasing frequency (lower opacity at mm-wavelength),   mm-VLBI  allows us to probe deeper into the self-absorbed regions of AGN, which is not possible at the longer cm-wavelengths.  Our group operates the Global Millimeter VLBI Array (GMVA), which combines up to 14 telescopes into regular 3mm/7mm VLBI observations and is a key partner for the Event Horizon Telescope (EHT), which performes VLBI observations at 1.3mm wavelength.  Both 3.5mm and 1.3mm VLBI observations may include the ALMA telescope.  One of the main goals of this effort is to probe the ‘the black hole shadows’ in the Galactic Centre and in the radio-galaxy M 87. Another important topic is to study the origin of jets and the initial jet acceleration and collimation in more distant radio-galaxies and quasars (AGN) with unprecedented resolution.

The PhD candidate will actively participate in the VLBI imaging of Active Galactic Nuclei (Quasars, BL Lac objects, Radio Galaxies, etc.) with the highest possible  angular and spatial resolution using the available VLBI arrays operating at millimeter wavelength (VLBA, HSA, GMVA, EHT). The research addresses questions related to AGN activity, outburst-ejection relations, the physical  origin of jets, the details of the jet launching and the primary jet acceleration  processes. For this the jet kinematics, their spectral and polarimetric properties will be studied using mm-VLBI images obtained from a variety of observing dates, and on spatial scales which are as close as possible to the central engine  (scales of a few 10 – 1000 gravitational radii).

Another science topic, within the scope of the M2FINDERS program (see below) is the study of the polarised fine structure of AGN, which probes the orientation and nature of magnetic fields at the innermost part of their relativistic jets.  mm-VLBI has the advantage that polarimetric observations at the shortest wavelengths are only marginally affected by Faraday rotation and probe the intrinsic linearly polarised emission.  We aim to probe if and how oblique shocks  in the innermost  jet regions  are responsible for the observed polarised emission. The detailed study of the three-dimensional, spatially bent  complex structure of the jet close to its nozzle  will help us to answer one of the most fundamental questions in AGN physics, which is how Black Holes launch relativistic jets.

Bibliography

  • Boccardi, B., Krichbaum, T.P., Ros, E., Zensus, J.A.: Radio observations of active galactic nuclei with mm-VLBI, A&ARv 25 4 (2017), https://doi.org/10.1007/s00159-017-0105-6
  • Tilanus, R.P.J., Krichbaum, T.P., Zensus, J.A., et al: Future mmVLBI Research with ALMA: A European vision, arXiv:14060.4650 (2014) https://arxiv.org/abs/1406.4650
  • Kim, J.-Y., Krichbaum, T., Lu, R.-S., Ros, E., Bach, U., Bremer, M., de Vicente, P., Lindqvist, M., Zensus, J.A.: The limb-brightened jet of M87 down to the 7 Schwarzschild radii scale, A&A 616, A188 (2018) https://doi.org/10.1051/0004-6361/201832921
  • Janssen, M., Falcke, H., Kadler, M., Ros, E., et al: Event Horizon Telescope observations of the jet launching and collimation in Centaurus A, Nature Astronomy (2021), https://doi.org/10.1038/s41550-021-01417-w
  • Lu, R.S., Krichbaum, T.P., Roy, A.L.: Detection of Intrinsic Source Structure at ˜3 Schwarzschild Radii with Millimeter-VLBI Observations of Sgr A*, Astroph. J. 859, 60 (2018) https://doi.org/10.3847/1538-4357/aabe2e
  • The Event Horizon Telescope Collaboration et al.: First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole, ApJL 875 L4 (2019), https://doi.org/10.3847/2041-8213/ab0e85
  • The Event Horizon Telescope Collaboration et al.: First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole, ApJL 875 L1 (2019), https://doi.org/10.3847/2041-8213/ab0ec7

Links

M2FINDERS project: www.mpifr-bonn.mpg.de/m2finders

Global mm-VLBI Array: www.mpifr-bonn.mpg.de/div/vlbi/globalmm

Event Horizon Telescope: www.eventhorizontelescope.org

Contact

Prof. Dr. J. Anton Zensus (azensus@mpifr.de), Dr. Thomas P. Krichbaum (tkrichbaum@mpifr.de),  Prof. Dr. Eduardo Ros (ros@mpifr.de), Dr. Michael Janßen (mjanssen@mpifr-bonn.mpg.de)

Very-long-baseline observations are the only direct evidence for relativistic outflows from supermassive black holes in active galactic nuclei (AGN).  The MOJAVE (north) and TANAMI (south) programs provide long-term, systematic monitoring of relativistic motion in AGN on parsec-scales.  These observations aim to characterize the kinematics and evolution of AGN jets and to determine how these relate to other source properties.  The MOJAVE data, together with the Boston University Blazar Monitoring survey also address the polarised emission and the morphology of magnetic fields in jets.  A large amount of information of the high-energy photons emitted by blazars is coming from the all-sky observations provided by the Large Area Telescope onboard the Fermi Gamma-Ray Observatory.

The proposed project will deal with the analysis of data from the monitoring surveys and to compare the radio properties determined from the VLBI observations (related to jet opacity, kinematics, magnetic field, etc.) with the properties derived at other bands of the spectrum, especially in x and γ rays, and even beyond it, as it is the case for high-energy neutrinos.

Bibliography

  • Ros, E., Kadler, M., Perucho, M. et al: Apparent superluminal core expansion and limb brightening in the candidate neutrino blazar TXS 0506+056, A&A 633, L1 (2020) https://doi.org/10.1051/0004-6361/201937206
  • Lister, M.L., Homan, D.C., Hovatta, T., et al.: MOJAVE. XVII. Jet Kinematics and Parent Population Properties of Relativistically Beamed Radio-loud Blazars:, ApJ 784, 43 (2019) https://doi.org/10.3847/1538-4357/ab08ee
  • Lister, M.L., Aller, M.F., Aller, H.D., et al.: Why have many of the brightest radio-loud balazars not been detected in gamma-rays by Fermi?, ApJ 810 L9 (2015) https://doi.org/10.1088/2041-8205/810/1/L9
  • Angioni, R., Ros, E., Kadler, M.: Gamma-ray emission in radio galaxies under the VLBI scope. I. Parsec-scale jet kinematics and high-energy properties of γ-ray-detected TANAMI radio galaxies, A&A 627 A148 (2019) https://doi.org/10.1051/0004-6361/201935697

Contact

Prof. Dr. Anton Zensus (azensus@mpifr.de), Prof. Dr. Eduardo Ros (ros@mpifr.de), Prof. Dr. Matthias Kadler (Univ. Würzburg, Germany, Matthias.kadler@astro.uni-wuerzburg.de)

Links

The MOJAVE Program: http://www.physics.purdue.edu/astro/MOJAVE/

The TANAMI Program: http://pulsar.sternwarte.uni-erlangen.de/tanami/

Site

Bonn, Max-Planck-Institut für Radioastronomie, VLBI Group in collaboration with the Universität Würzburg, the NASA Goddard Flight Space Centre, Aalto University, and other centres of the MOJAVE and TANAMI collaborations.

Extragalactic jets are formed in the environments of supermassive black holes (SMBH) in active galactic nuclei (AGN). They are among the most powerful and energetic astrophysical objects. Their relevance is not only due to their role as laboratories of relativistic plasmas, but they also have an important effect in their environments, namely, in the interstellar medium of the host galaxy and the intergalactic medium. Understanding their nature and physics can thus give us key information about the progenitor SMBH and its surroundings, but also about the host galaxy and its history. A combination between detailed VLBI observations and theoretical modelling via numerical simulations has proven to be a very good approach to reach the goal of this research.

At present, we are able to perform numerical simulations in supercomputers, including all the relevant physics of these objects: relativistic gas, magnetic fields, different compositions. We have the tools to convert these models into synthetic data for a direct comparison with observations. VLBI is addressing the innermost radio structure of these objects, and gives the observational input to theoretical studies.  Here we propose to continue an already started line of research, which consists in trying to relate the emitting, non-thermal population of particles, studied through observations, with the thermal gas in the jet and the magnetic fields, responsible for the macroscopic jet dynamics.  The role of magnetic fields and its signature in the polarised emission, which can be simulated for the plasma physics and for the emission processes, is one of the goals of the M2FINDERS project (see below).

Bibliography

  • Fromm, C. M., Younsi, Z., Baczko, A.K., Mizuno, Y., Porth, O., Perucho, M., Olivares, H., Nathanail, A., Angelakis, E., Ros, E., Zensus, J.A., Rezzolla, L.: Using evolutionary algorithms to model relativistic jets – Application to NGC 1052, A&A 629 A4 (2019), https://doi.org/10.1051/0004-6361/201834724
  • Fromm, C. M., Perucho, M., Porth, O., Younsi, Z., Ros, E,; Mizuno, Y., Zensus, J. A., Rezzolla, L.: Jet-torus connection in radio galaxies. Relativistic hydrodynamics and synthetic emission, A&A (2018) 609 A80, https://doi.org/10.1051/0004-6361/201731048
  • Fromm, C. M.; Perucho, M.; Mimica, P.; Ros, E.: Spectral evolution of flaring blazars from numerical simulations, A&A (2016) 588, A101, https://doi.org/10.1051/0004-6361/201731048
  • Perucho, M.; Agudo, I.; Gómez, J. L.; Kadler, M.; Ros, E.; Kovalev, Y. Y.: On the nature of an ejection event in the jet of 3C 111, A&A (2009) 489, L59, https://doi.org/10.1051/0004-6361:200810479
  • Roelofs, F.; Janssen, M.; Natarajan I.; Deane R.; Davelaar, J.; Olivares, H.; Porth, O.; Paine, S. N.; Bouman, K. L.; Tilanus, R. P. J; van Bemmel, I. M.; Falcke H., et al. (The Event Horizon Telescope Collaboration): SYMBA: An end-to-end VLBI synthetic data generation pipeline. Simulating Event Horizon Telescope observations of M87, A&A (2020) 636, A5, https://doi.org/10.1051/0004-6361/201936622

Links

M2FINDERS project: www.mpifr-bonn.mpg.de/m2finders

Contact

Prof. Dr. Anton Zensus (azensus@mpifr.de), Prof. Dr. Eduardo Ros (ros@mpifr.de ), Dr. N. MacDonald (nmacdona@mpifr.de), Prof. Dr. Manel Perucho (Univ. València, Spain, perucho@uv.es ), Dr. Christian M. Fromm (Universität Würzburg, cfromm@th.physik.uni-frankfurt.de ),  Dr. Michael Janßen (mjanssen@mpifr-bonn.mpg.de)

Site

Bonn, Max-Planck-Institut für Radioastronomie, VLBI Group in collaboration with the Universitat de València, Spain and the Universität Würzburg

Prominent jets in active galactic nuclei are believed to be powered by the enormous amount of energy released in the regions surrounding the central supermassive black holes. Understanding the physical mechanism of the generation and transport of this energy is crucial for both building a self-consistent picture of extragalactic relativistic jets and uncovering the ultimate nature of the cosmic black holes. Theoretical explanations relate the production and outward transport of energy to black hole rotation, accretion disks, relativistic plasma jets, and magnetic fields. The latter are also expected to be responsible for the commonly observed edge-brightening of jets. At radio wavelengths, where VLBI observations achieve highest-resolution imaging, one can trace the strongly collimated relativistic jets down to linear scales of a few lightdays. Observations with the Event Horizon Telescope have now made it possible to image the immediate vicinity of the suspected black holes on event horizon scales. This project will address a major remaining astronomical challenge in the AGN puzzle and potentially the most crucial piece of the unequivocal proof of the very existence of black holes: measuring with sufficient precision the strength and three dimensional structure of the magnetic fields on scales smaller than 1000 gravitational radii from the central black hole in order to answer the questions how jets are launched and powered.  The project will combine (i) high-resolution multi-frequency polarimetric VLBI radio imaging and (ii )opacity measurements for a sample of AGN jets with advanced analytical and numerical modelling of relativistic flows. This combination has the best potential for yielding unprecedented constraints on the theoretical models for cosmic black holes and the production of extragalactic relativistic jets.

Bibliography

Links

M2FINDERS project: www.mpifr-bonn.mpg.de/m2finders

Contact

Prof. Dr. Anton Zensus (azensus@mpifr.de), Prof. Dr. Eduardo Ros (ros@mpifr.de), Dr. Andrei Lobanov (alobanov@mpifr.de),  Dr. Michael Janßen (mjanssen@mpifr-bonn.mpg.de)

Site

Bonn, Max-Planck-Institut für Radioastronomie, VLBI Group, in collaboration with the Universitat de València, Spain and the Goethe-Universität Frankfurt.

The study of the linear and circular polarization in the nuclei of active galaxies (AGN) allows one to gain detailed information about the properties of the magnetic fields and the magnetized plasma in these objects and their emanating jets. This is important to better understand how Black Holes launch radio-jets and how radio-jets propagate.  Rotation measure (RM) Synthesis is a new tool for the interpretation of polarized emission data in order to obtain more information on the emitting plasma and the intermediate Faraday Screen(s), which can alter the source intrinsic polarisation. Such Faraday screens can be related directly to the accretion flow onto the central black hole, but also to the radio jets, their surrounding matter, and the intervening intergalactic medium between the observer and the galaxy.  In this project we want to apply this method to the highly variable group of Blazars, most of which are also being imaged in parallel with local interferometers (NOEMA, ALMA) and with VLBI. These Blazars are extragalactic radio sources, which show prominent emission from ultra-relativistic jets. They emit over the whole range of the electromagnetic spectrum, from radio bands to the highest energies (Gamma-rays, TeVs). Polarisation and Rotation Measure observations can help to better understand the physical conditions in these Blazars, and their relation to the high energy emission production processes.

This PhD project will focus on the study of AGN polarisation and its variability over the frequency bands which are covered by the Effelsberg radio telescope. Special emphasis is given to polarisation measurements using the higher frequencies, in particular the receivers which cover the 15-50 GHz band. In this band, polarisation measurements were not possible before and some new discoveries can be expected with the new broad band spectro-polarimeter, which was recently installed at the 100m radio telescope. Besides the science research on AGN polarisation, the candidate is expected to actively help characterize the new SPECPOL polarimeter, perform systematic studies on the frequency dependent instrumental polarisation of the receiving system, and refine the calibration strategies towards a further improved polarimetric performance.

Bibliography

  • Angelakis, E., Fuhrmann, L., Myserlis, I., et al.: Multi-frequency radio monitoring of Fermi blazars. The 2.64 to 43 GHz Effelsberg light curves from 2007-2015, AA, 626, 60 (2019), https://ui.adsabs.harvard.edu/abs/2019A%26A…626A..60A/abstract
  • Myserlis, I., Angelakis, E., Kraus, A., et al.: Full-Stokes polarimetry with circularly polarized feeds. Sources with stable linear and circular polarization in the GHz regime, A&A, 609, 68 (2018), https://ui.adsabs.harvard.edu/abs/2018A%26A…609A..68M/abstract
  • Cenacchi, E., Kraus, A., Orfei, A., Mack, K.-H.: Full-Stokes polarimetric observations with a single-disk radio telescope, AA, 498, 591 (2009), https://ui.adsabs.harvard.edu/abs/2009A%26A…498..591C/abstract
  • Brentjens, M.A., de Bruyn, A.G.: Faraday Rotation Measure Synthesis, AA, 441, 1217 (2005),  https://ui.adsabs.harvard.edu/abs/2005A%26A…441.1217B/abstract

Links

The 100m Effelsberg Telescope: https://www.mpifr-bonn.mpg.de/effelsberg/astronomers

Contact

Prof. Dr. J. Anton Zensus (azensus@mpifr.de), Dr. Thomas Krichbaum (tkrichbaum@mpifr.de), Dr. A. Kraus (akraus@mpifr.mpifr.de), Dr. U. Bach (ubach@mpifr.de)

Site

Bonn, Max-Planck-Institut für Radioastronomie, VLBI group in collaboration with the Effelsberg Observatory and  the Universität zu Köln.

AZ07: Millimeter-VLBI studies of gamma-ray bright radio galaxies

Nearby radio galaxies are ideal laboratories to study the physical processes occurring in the vicinity of supermassive black holes. In radio galaxies, unlike in blazars, projection and relativistic effects have a mild impact on the observed jet emission, which enables us to more easily infer the intrinsic jet properties and to probe emitting regions which would be, otherwise, hidden.

The goal of the proposed PhD project is to obtain a broad overview of the high-energy emission processes in relativistic jets, in relation to the AGN accretion properties and the jet power. The focus will be on millimeter-VLBI studies of radio galaxies detected by the Fermi-LAT telescope at gamma-ray energies. While previous analyses have been limited to a few case studies, several new radio galaxies have been recently identified as gamma-ray emitters. Millimeter-VLBI observations will be used to characterize the jet internal structure and, in combination with multi-frequency data, to pinpoint the high-energy emission sites. This provides a wealth of information which will be used to model the broadband emission and constrain the gamma-ray emission mechanisms.

Bibliography:

  • Boccardi, B., Migliori, G., Grandi, P., et al.:  The TeV-emitting radio galaxy 3C 264. VLBI kinematics and SED modeling, A&A (2019) 627 89,  https://doi.org/10.1051/0004-6361/201935183
  • Casadio, C., Gomez, J.L., Grandi, P., et al. : The Connection between the Radio Jet and the Gamma-ray Emission in the Radio Galaxy 3C 120, ApJ (2015) 808 162

Links:
Global mm-VLBI Array: www.mpifr-bonn.mpg.de/div/vlbi/globalmm

Contact:
Dr. Bia Boccardi (bboccardi@mpifr.de), Prof. Dr. J. Anton Zensus (azensus@mpifr.de)

Site:
Bonn, Max-Planck-Institut für Radioastronomie, VLBI Group, in collaboration with the Universitat de València, Spain and the University of Bologna, Italy.

Millimeter and Submillimeter Astronomy Group at the MPIfR

Director: Prof. Dr. Karl Menten

Group Website

The Heterodyne Instrument for the Far-Infrared (HIFI) abord Herschel opened a whole new era of studies of the diffuse interstellar medium (ISM). Utilizing Herschel’s superb sensitivity combined with its high spectral resolution receivers operating in a low thermal background space environment, HIFI revolutionized observations of light hydrides, many of which have their ground-state rotational transitions in the submillimeter and far infrared range. As the building blocks of larger molecules, the (mostly) di- or triatomic species detected by HIFI and (also by APEX and SOFIA) are of central astrochemical interest. In addition, they triggered new interest in the physics and chemistry of diffuse and translucent clouds, for example in their role as interfaces between the cold (and warm) neutral atomic and the denser, cold molecular phases of the ISM in our, but also in external galaxies.

Building on the success of Herschel, new opportunities arise with ground-based and airborne observations of hydrides: in the submillimeter range, hydrides such as 13CH+, OH+, and SH+ can be studied using the APEX telescope with new receivers and the exceptional atmospheric conditions on the Chajnantor Plateau in northern Chile. Access to even higher frequencies is provided by the airborne Stratospheric Observatory for Infrared Astronomy (SOFIA) and the GREAT receiver and allows observations of CH, SH and OH, to name just a few of the simplest hydrides. A thorough analysis of such observations will lead to a comprehensive characterization of hydrides in diffuse clouds throughout our Galaxy.

Possible dissertation projects comprise observational studies with, predominantly, SOFIA and APEX, but also with other telescopes as well modeling of the data and bringing them into context with a glabal view of the Milky Way galaxy’s ISM.

Contact: Prof. Dr. Karl Menten (kmenten@mpifr-bonn.mpg.de)
Site: Bonn, Max-Planck-Institut für Radioastronomie

The unprecendented sensitivity and large bandwidth (8GHz) of the new Effelsberg K-band receiver, covering 18-26 GHz in frequency, offer new opportunities to study the physical and chemical conditions of star forming regions and mant other interesting sources with unbiased line surveys. These surveys give access to probes of temperature, density and chemistry that can be used to characterize the evolutionary stages of the regions. The project will be very complementary to line survey projects conducted with the IRAM 30m and APEX 12m telescopes in the millimeter and submillimeter wavelength range, respetively.

The K-band contains many interesting lines, amongst them the many transitions of ammonia (including 15NH3 and non-metastable lines), as well as lines from carbon chains like HC3N, HC5N (for both also isotopologues and vibrationally excited levels), from molecules like methanol, CCS, C3H2, C6H and several recombination lines and maser transitions (water, methanol, ammonia), make K-band line surveys very appealing for molecular fingerprints, that can be used to rapidly characterize the main charactistics and the evolutioniary stage of the regions, then leading to a new “K-band spectral classification” of star forming regions.

For such surveys, a sophisticated data reduction pipeline, capable of processing and calibrating the large amount of data will be needed. The PhD candidate will participate in setting up this pipeline to prepare for the analysis of the wealth of molecular line data. A background in software engineering and experience with data reduction of radio astronomical data would be a plus.

Contact: Dr. Friedrich Wyrowski (wyrowski@mpifr.de), Dr. Benjamin Winkel (bwinkel@mpifr.de), Dr. A. Kraus (akraus@mpifr.de) Prof. Dr. Karl Menten (kmenten@mpifr-bonn.mpg.de)
Site: Bonn, Max-Planck-Institut für Radioastronomie

Studying the physical and chemical processes occurring in the nuclear regions of galaxies is of fundamental importance for understanding the formation, evolution and dynamics of galaxies. Many galaxies, including our Milky Way, contain huge amounts of gas in their central hundred parsecs. This molecular and atomic material is strongly affected by the presence of the large potential gradients, X-rays, cosmic rays, and magnetic fields. These extreme conditions result in the well known properties of the molecular clouds in our Galactic center, such as the large velocity widths, high kinetic temperatures and the high chemical complexity observed in this region.

At ~8 kpc from us, the center of our Galaxy presents a unique laboratory to study the phenomena occurring in the heart of the galaxies with high spatial resolution. APEX and ALMA with their location in the southern hemisphere, which allows 11 h of observing time per day, and the excellent weather conditions at the Chajnantor site, are unique telescopes to study the Galactic center in the submm regime.

In this ambitious project the large scale kinematics and the unique physical and chemical conditions in the Central Molecular Zone will be studied with new muti-beam receiver arrays on the APEX telescope. ALMA will be used for a high angular resolution view of selected regions.

Contact:  Prof. Dr. Karl Menten (kmenten@mpifr-bonn.mpg.de)
Site: Bonn, Max-Planck-Institut für Radioastronomie, Millimeter and Submillimeter Astronomy Group

Understanding the circumstances of massive star formation is one of the great challenges of modern astronomy. In the last years, our view of massive star forming regions has dramatically been changed by Galactic plane surveys covering centimeter to infrared wavelengths. These surveys enable us for the first time to study ALL evolutionary stages of massive star formation in an unbiased way. With the exciting results of the new submm/FIR surveys from the ground (ATLASGAL) and space (Hi-GAL) the massive and cold dust clumps from which massive cluster form are now detected in an unbiased way. Complementary, the EVLA will allow incredibly powerful and comprehensive radio- wavelength surveys of, both, the ionized and the molecular tracers of star formation in the Galactic plane.

In this project, the extremely wideband (4-8 GHz) new C-band receivers of the EVLA will be used for an unbiased survey to find and characterize star-forming regions in the Galaxy.  This survey of the Galactic plane, that is now ongoing, will detect tell-tale tracers of star formation: compact, ultra-, and hyper-compact Hii regions and molecular masers which trace different stages of early stellar evolution and will pinpoint the very centers of the early phase of
star-forming activity. Combined with the submm/infrared surveys it will offer a nearly complete census of the number, luminosities and masses of massive star forming clusters in a large range of evolutionary stages and provide a unique dataset with true legacy value for a global perspective on star formation in our Galaxy.

Contact: Dr. Friedrich Wyrowski (wyrowski@mpifr- bonn.mpg.de), Prof. Dr. Karl Menten (kmenten@mpifr-bonn.mpg.de)

Site: Bonn, Max-Planck-Institut für Radioastronomie, Millimeter and Submillimeter Astronomy Group

The very successful APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) has revealed for the first time the structure of the cold interstellar medium over several 100 sq. deg. The survey was conducted with LABOCA at the APEX telescope to conduct an unbiased census of massive star forming clumps and their different evolutionary stages in the inner Galaxy.

Soon a new, much larger bolometer camera will be commissioned at the APEX telescope, the A-MKID dual color camera with ~3500 pixel at 870 and ~20000 pixel at 350 micrion. At the short wavelengths, this instrument will allow to resolve sources of 0.1 pc size within 3 kpc towards giant star forming complexes.  When combining the A-MKID data with the Herschel/Hi-GAL survey at 60 to 600 micron, it will be possible to:

• derive evolutionary stages for a representative sample of star forming clumps

• compute dust emissivity and temperature over a large star forming complex

• analyze how the physical conditions vary within one giant complex

• study the fragmentation of clumps into cores that can give birth to individual stars

Given its high angular resolution and unbiased nature, such a survey

will provide a legacy and pathfinder for years to come.

Contact: Dr. Friedrich Wyrowski (wyrowski@mpifr- bonn.mpg.de), Prof. Dr.Karl Menten (kmenten@mpifr-bonn.mpg.de)

Site: Bonn, Max-Planck-Institut für Radioastronomie, Millimeter and Submillimeter Astronomy Group

Massive stars form in dense clumps within giant molecular clouds (GMCs), but how do these clouds form and evolve, how do the dense clumps form within them and what are the conditions for star formation within these dense clumps? To address these questions the MPIfR operates powerful heterodyne cameras for line observations, such as the upcoming new LAsMA array for observations at 345GHz and the CHAMP+ array (690 and 810 GHz), both at APEX, complemented by the upGREAT array on SOFIA for THz observations of important fine structure cooling lines. The high mapping speed of these cameras enables to map giant molecular clouds on degree scales in a variety of molecules. Such a chemical inventory provides a new view on the large scale properties of molecular clouds. Furthermore, by combining results from the different cameras the excitation and cooling of the clouds can be constrained to form a comprehensive picture of the formation and condition in GMCs.

Some of scientific questions to tackle with these observations are: What is the dynamics of the clouds and the embedded clumps? How strongly are the chemical conditions in the clouds altered by interaction processes, either from the outside of the clouds or by feedback from the ongoing star formation in the clouds? Can some of the chemical variations be used in conjunction with chemical models as chemical clocks to put different clumps in the clouds into an evolutionary sequence? How do these large-scale chemical properties of Galactic GMCs compare with observations of their extra-galactic counterparts that are now feasible with the high sensitivity and angular resolution of ALMA?

Contact: Dr. Friedrich Wyrowski (wyrowski@mpifr-bonn.mpg.de), Prof. Dr.Karl Menten (kmenten@mpifr-bonn.mpg.de)
Site: Bonn, Max-Planck-Institut für Radioastronomie, Millimeter and Submillimeter Astronomy Group

The Argelander Institute for Astronomy at the U of Bonn

Research Groups: http://www.astro.uni-bonn.de/en/research/groups/

The most massive stars, assuming mass loss is not too strong, are thought not to form iron cores, but rather to become unstable due to electron-positron-pair formation before central oxygen burning. The collapsing oxygen-rich core will then ignite oxygen explosively, which may lead to pair-instability supernovae, leaving no compact remnant. While such explosions have been predicted since 50 years ago, they were often assumed to only occur in the early universe. However, very recently, pair- instability supernovae have been found observationally in the local universe. This PhD project aims at constructing the first progenitor and explosion models for local, i.e., finite metallicity pair-instability supernovae, using our most modern hydrodynamic stellar evolution code. The idea is to characterize the observable properties of the progenitor and of the supernovae, and to make predictions for the nucleosynthesis yields of pair-instability, which could well dominate the metal production in their host galaxies.

Bibliography:

Gal-Yam, A., et al., 2009, Nature, 462, 624

Langer, N., 2009, Nature, 462, 579

Contact: Prof. N. Langer (nlanger@astro.uni-bonn.de)

Site: Bonn, Bonn, Argelander Institute for Astronomy, University of Bonn

Dark energy makes up about 70% of the Universe’s energy content and is responsible for its observed acceleration. A powerful method to constrain this enigmatic component is a precise measurement of the evolution of the most massive objects in the Universe: galaxy clusters. For this purpose, the new X-ray telescope eROSITA has been launched in July 2019. Its mission is the discovery of ~100,000 galaxy clusters, including ALL massive clusters in the entire observable universe. eROSITA will be the first “Stage IV” dark energy probe world-wide. The PhD candidate will enjoy privileged access to the first eROSITA data to study galaxy cluster physics, chemistry, and cosmology.

Bibliography:

Contact: Prof. Dr. Thomas H. Reiprich (reiprich@astro.uni-bonn.de)

Site: Bonn, Argelander Institute for Astronomy, University of Bonn

Our group explores how the gas physical conditions and chemistry (gas densities, pressures, temperatures, abundances) 
connect to the ability of individual, nearby galaxies to convert this gas into stars. We explore how different 
galaxies differ in the ability to form stars, but also the local gas physics and dynamics within individual 
galaxies and their role in triggering the formation of new stars. Our main focus is observational, specifically 
atomic and molecular gas spectral line observations as well as cooling lines in the far-infrared to constrain gas 
physics (increasingly also chemistry) and star formation rates within and among local galaxies. This includes 
observing campaigns with state of the art facilities, like ALMA, the IRAM 30m telescope and the NOEMA 
interferometer as well as the VLA, Meerkat or SOFIA in the infrared. We combine such observations with modelling 
(radiative transfer, astrochemistry) as well as with complementary observations in the Milky Way to shed light 
on the big questions: "what regulates star formation across galaxies?" and "how do galaxies evolve over cosmic 
time?”. There are always thesis opportunities in our group so that we encourage interested students to apply.
Exemplary References:

  • Bigiel et al., ApJ, in press, 2020
  • Barnes, Kauffmann, Bigiel, et al., 2020, MNRAS, 497, 1972
  • Jimenez-Donaire, Bigiel, et al. 2019, ApJ, 880, 127
  • Cormier, Bigiel et al. 2018, MNRAS, 475, 3909
  • Gallagher, Leroy, Bigiel et al. 2018, ApJ, 858, 90

Website: https://astro.uni-bonn.de/de/forschung/radioastronomy-ism

contact: Frank Bigiel (bigiel@astro.uni-bonn.de)
location: Bonn University

 

Traditional studies of the large-scale structure of the Universe are based on two-point statistics like the power spectrum. However, the galaxy distribution is highly non Gaussian and precious information is stored in its higher-order correlation functions (and their Fourier transforms, the multi-spectra). This project aims to develop theoretical models and statistical methods to extract cosmological information from the analysis of (new and old) higher-order statistics of the galaxy distribution. It involves a combination of numerical simulations and analytical techniques. This project will be conducted within the activities of the Higher-order Statistics work package of the Galaxy Clustering working group of the Euclid consortium.

Literature:

Yankelevich & Porciani “Cosmological information in the redshift-space bispectrum” https://arxiv.org/abs/1807.07076
Oddo et al. “Toward a robust inference method for the galaxy bispectrum: likelihood function and model selection” https://arxiv.org/abs/1908.01774
Kuruvilla & Porciani “The n-point streaming model: how velocities shape correlation functions in redshift space” https://arxiv.org/abs/2005.05331

Contact: Prof. Dr. Cristiano Porciani (porciani@astro.uni-bonn.de)
Site: Bonn, Bonn, Argelander Institute for Astronomy, University of Bonn

Computer simulations play a key role as a complement to observations in astrophysics and cosmology.
Our group is at the forefront of the development and application of innovative numerical techniques. We regularly have access to some of the most powerful HPC facilities. Several Ph.D. projects along different lines of research are available. For instance,
– performing constrained simulations to study the effect of the environment onto structure and galaxy formation;
– modelling molecule and dust formation in simulations of galaxy assembly;
– improving models of stellar feedback in simulations of galaxy formation;
– simulating the epoch of reionisation with hydrodynamic simulations including radiative transfer.

Literature:

Borzyszkowski et al. “ZOMG – I. How the cosmic web inhibits halo growth and generates assembly bias”  https://arxiv.org/abs/1610.04231
Garaldi et al. “The Goldilocks problem of the quasar contribution to reionization” https://arxiv.org/abs/1809.10144
Schäbe et al. “A comparison of H2 formation models at high redshift” https://arxiv.org/abs/2003.04329

Contact: Prof. Dr. Cristiano Porciani (porciani@astro.uni-bonn.de)
Site: Bonn, Bonn, Argelander Institute for Astronomy, University of Bonn

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 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.

Bibliography

  • “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

Contact: Dr. Kaustuv Basu (kbasu@astro.uni-bonn.de), Prof. Dr. Frank Bertoldi (bertoldi@astr.uni-bonn.de)

Site: Bonn, Argelander Institute for Astronomy, University of Bonn

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 starting from 2021.

References:
1. “CCAT-Prime: science with an ultra-widefield submillimeter
observatory on Cerro Chajnantor”
G. Stacey et al. 2018, SPIE proceedings, arXiv:1807.04354

2. “Planck’s view on the spectrum of the Sunyaev-Zeldovich effect”
J. Erler et al. 2018, MNRAS, arXiv:1709.01187

Bibliography:

  • “A Space Mission to Map the Entire Observable Universe using the CMB as a Backlight”, K. Basu et al., ESA Voyage 2050 Science Paper, arXiv:1909.01592
  • “SZ spectroscopy” in the coming decade: Galaxy cluster cosmology and astrophysics in the submillimeter”, K. Basu et al., Astro2020 White Paper, arXiv:1903.04944

Contact: Dr. Kaustuv Basu (kbasu@astro.uni-bonn.de), Prof. Dr. Frank Bertoldi (bertoldi@astro.uni-bonn.de)

Site: Bonn, Argelander Institute for Astronomy, University of Bonn

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 PhD student will participate in the transregional collabroative research center TRR 33 “Tha Dark Universe” and in the activities of the German ARC node.

Reference: “ALMA-SZ Detection of a Galaxy Cluster Merger Shock at Half the Age of the Universe”, K. Basu et al., ApJ 829, 2016, arXiv:1608.05413

Contact: Prof. Dr. Frank Bertoldi (bertoldi@astro.uni-bonn.de), Dr. Kaustuv Basu (kbasu@astro.uni-bonn.de)

Site: Argelander-Institute for Astronomy, University of  Bonn

ESA’s space probe Euclid, currently scheduled for launch in 2022, will constrain the cosmological model and study the nature of dark energy using two techniques: weak gravitational lensing and redshift space distortions. Our group at the AIfA is involved in the scientific preparation of the mission, in particular the development of techniques for weak lensing galaxy shape measurements that require careful correction for instrumental distortions such as the image point-spread function (PSF). One focus of our activities is on exploiting the Hubble Space Telescope (HST) archive as a training sample for weak lensing shape measurements. We are developing a shape measurement method for Euclid based on machine learning and are characterizing the impact of residual detector effects on the shape analysis. As an additional focus, we plan to work on Euclid weak lensing measurements of galaxy clusters. We are looking for a PhD student to join our team. One focus of our activities is on exploiting the Hubble Space Telescope (HST) archive as training sample for weak lensing shape measurements. We are also developing a shape measurement method for Euclid based on machine learning. Furthermore, we are characterizing the impact of residual detector effects on the shape analysis. As an additional focus, we plan to work on Euclid weak lensing measurements of galaxy clusters.
Literature:
Schneider, P. (2006), “Weak gravitational lensing”, arXiv:astro-ph/0509252
Hernandez-Martin et al. (2020): “Constraining the masses of high-redshift clusters with weak lensing: Revised shape calibration testing for the impact of stronger shears and increased blending”, https://arxiv.org/abs/2007.00386
Laureijs, R. et al. (2011), “Euclid definition study report”, arXiv:1110.3193L

Tewes, M. et al. (2019), “Weak-lensing shear measurement with machine learning. Teaching artificial neural networks about feature noise.”,  arXiv:1807.02120
Euclid Collaboration et al. (2019): “Euclid preparation. IV. Impact of undetected galaxies on weak-lensing shear measurements”, arxiv:1902.00044

Contact: Dr. Tim Schrabback (schrabba@astro.uni-bonn.de), Prof. Dr. Peter Schneider (peter@astro.uni-bonn.de)
 
Site: Bonn, Argelander Institute for Astronomy, University of Bonn

Research Groups: https://www.astro.uni-koeln.de/

Over the past two decades, observational studies of the cosmic histories of star formation, stellar mass, and interstellar gas (i.e. the fuel for star formation) and their theoretical underpinning have revealed that feedback is an integral part of the galaxy formation process. Yet, the physical properties, timescales, and key mechanisms remain poorly understood. This project focuses on observational multi-wavelength studies of the physical properties and chemical composition of the interstellar gas and dust involved in the star formation process, and the potential role of active galactic nuclei in the regulation of the fuel supply. Rich new data sets are readily available and ripe for exploration or scheduled for observation at the Atacama Large (sub-)Millimeter Array (ALMA), the NOrthern Extended Millimeter Array (NOEMA), the Karl G. Jansky Very Large Array (VLA), the James Webb Space Telescope (JWST), and supporting facilities. The successful candidate will also have the opportunity to participate in large international collaborations as part of their research efforts.

Contact: Prof. Dr. Dominik A. Riechers (riechers@ph1.uni-koeln.de)
Site: I. Physikalisches Institut, Universität zu Köln

One of the few remaining poorly understood eras in the history of the Universe is the Epoch of Cosmic Reionization (EoR), which took place approximately 300 million years to one billion years after the Big Bang. Current observational constraints suggest that the reionization process, during which the intergalactic neutral hydrogen gas that filled the universe since recombination at 380,000 years after the Big Bang was once again ionized, was largely driven by ultraviolet photons
emerging from the first stars and galaxies, which were faint but very numerous. While many models treat reionization as a quasi-instantaneous process given the current dearth of direct observational constraints, it is more likely to be a process stretching out over hundreds of millions years, where the exact timing
depends on the local galaxy density and the physical properties of the first stars and galaxies.

Starting in 2023, the new CCAT-prime submillimeter observatory (in which the University of Cologne is a founding partner), built at 5600m elevation in the Chilean desert, will carry out a dedicated 4000 hour survey to constrain the topology of reionization by measuring the clustering of star-forming galaxies at the same time. The survey will target atomic fine structure lines from the neutral and ionized gas in the star-forming regions, which characterize their intrinsic properties and the occurrence rate of ionizing photons from newly-formed massive stars. The successful candidate will have the opportunity to participate in the preparation of the survey, observing, and exploitation of the incoming data set, which will yield fundamentally new constraints on our understanding of the very early Universe. Depending on interest, a participation in instrumentation efforts will also be possible. This effort is undertaken by a large international research collaboration which the candidate will join. While the project is situated in Cologne, close collaboration with the groups in Bonn (including modeling efforts) is
anticipated and encouraged.

Contact: Prof. Dr. Dominik A. Riechers (riechers@ph1.uni-koeln.de)
Site: I. Physikalisches Institut, Universität zu Köln