List of proposed PhD projects

 

 

 

 

 

PhD projects list for the call of November 15, 2013

 

Here follows a list of some representative PhD projects for applicants to the IMPRS for Astronomy and Astrophysics. In case of preference, please indicate the Project Codes in your application form. It must be made clear that all these are only optional and indicative. It is highly recommended that you contact the scientific staff of the involved institutes for further suggestions, discussion and topics.

 

The projects are organized in 6 groups each one of which corresponds to a scientific division of the participating institutes. Click the links below to jump to the corresponding group:

 

1.   Very Long Baseline Interferometry Group (MPIfR): AZ project list

2.     Millimeter and Sub-millimeter Group (MPIfR): KM project list

3.     Fundamental Physics in Radio Astronomy Group (MPIfR): MK project list

4.     University of Bonn: Uni. Bonn project list

5.     University of Cologne: Uni. Cologne project list

 

 

Note 1: At the end of each description there are links to link you back to the beginning of a group or the beginning of this document.

 

 

 

 

 

 

 

Very Long Baseline Interferometry Group

Director: Prof. Dr. J. Anton Zensus

                                                                                                         

Group website

 

 

Code: AZ01

TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry)

 

TANAMI is an international project done in collaboration with the Universities of Wrzburg and Valencia and NASA's Goddard Space Flight Center to monitor the parsec-scale structures of relativistic jets in active galactic nuclei in the Southern Hemisphere. The jets south of -30 deg declination are being monitored at 1.3 cm and 3.6 cm radio wavelengths by means of very-long-baseline interferometry.  TANAMI uses the Australian Long Baseline Array complemented with additional stations extended towards South Africa, the Antarctica and Chile. Observations started in 2007, prior to the launch of the gamma-ray Fermi satellite, which is also probing those sources in the other extreme of the spectrum, with the aim of relating the emission in the radio and at high energies. Correlated multiwavelength observations are being done with modern X-ray telescopes (XMM-Newton, Swift, INTEGRAL) as well as in the NIR/optical regime. The PhD project will investigate the nature of active galactic nuclei, their supermassive black holes and relativistic jets, making use of unprecedented data across the whole electromagnetic spectrum.

 

Project Aims:

The most powerful extragalactic jets of the Southern Hemisphere are being probed by Fermi in the gamma-ray regime, and by single-dish and interferometric TANAMI observations in the radio band.  The imaging and further analysis of individual sources and of the complete data set is planned in this PhD project: data debugging, image analysis, spectral studies of the jets, correlation study of the morphological and brightness variation in the context of a multi-band approach are the main goals of the project.  The data being collected are unique, for its quality and for coming from the relatively unexplored Southern skies.  The project guarantees integration in the NASA Fermi/LAT collaboration, high-impact publications and a long time baseline for collaboration, since Fermi/LAT will operate for the next 5-10 years, and TANAMI is expected to keep collecting data during this time.

 

Bibliography:

Ojha et al. A&A, 519, A45 (2010)

MPIfR Press Release (June 2011): http://www.mpifr-bonn.mpg.de/public/pr/pr-cena-may2011-dt.html

See full publication list at http://pulsar.sternwarte.uni-erlangen.de/tanami/pubs/

 

Contact: Prof. Dr. Anton Zensus (azensus@mpifr-bonn.mpg.de) and Prof. Dr. Matthias Kadler (matthias.kadler@astro.uni-wuerzburg.de), Prof. Dr. Eduardo Ros (ros@mpifr-bonn.mpg.de)

 

Site: Bonn, Max-Planck-Institut fr Radioastronomie, VLBI group In collaboration with the University of Wrzburg, Germany

 

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Code: AZ02

Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments

 

 About ten percent of the active galactic nuclei (AGN) eject jets of plasma at relativistic speeds from their central regions. The rapidly variable non-thermal emission and apparent superluminal motions in the jets imply that they contain highly energetic plasma moving nearly directly at us at speeds approaching that of light. Understanding the acceleration, collimation, and stability properties of these flows is one of the central topics in the modern relativistic astrophysics. High-dynamic-range, high-resolution radio imaging of (sub-)parsec-scale structures in the jets is essential to derive observational constraints for the physical conditions in the jets close their launching site.

 

Very long baseline interferometry (VLBI) imaging with its unsurpassed angular resolution allows direct studies of the innermost parsecs of the jets. The MOJAVE program (Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments) monitors structural changes in the parsec-scale jets of over 300 AGN making it one of the largest VLBI monitoring programs to date. The program is unique in its extent, time-sampling, and statistical completeness of the sample. Many of the monitored sources have over 15 years of well-sampled observations providing an unprecedented data set for studying the evolving jet structures.

 

The PhD candidate will join the international MOJAVE program team and use the survey data to analyze the properties of magnetized plasma jets in AGN. According to his/her interests, the candidate can concentrate e.g., on a statistical analysis of the observed structures of the jet and its magnetic field, or carry out an in-depth study of the time-evolution of the shocked regions in the jets of a few selected sources.

 

Contact: Prof. Dr. Anton Zensus (azensus@mpifr-bonn.mpg.de), Dr. Tuomas Savolainen (tsavolainen@mpifr-bonn.mpg.de), Prof. Dr. Eduardo Ros (ros@mpifr-bonn.mpg.de)

 

Site: Bonn, Max-Planck-Institut fr Radioastronomie, VLBI group

 

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Code: AZ03

From Black Holes to Jets: Active Galactic Nuclei

 

Very Long Baseline Interferometry in the radio regime (VLBI) provides highest resolution images of the central regions of Active Galactic Nuclei (AGN). In these inner parts of the most energetic objects of the Universe jets are created and collimated. The role of the accretion disk and the black hole in the launching of jets is still a matter of debate. Unification scenarios – relying on the same Jet/Accretion disk/Black Hole-system in all objects - explain different types of AGN as due to orientation effects. However, this cannot explain all observed jet-phenomena.

 

Project aims: The research for the PhD project concentrates on unusual phenomena in the jets of AGN in the vicinity of black holes. The current paradigm of "simple" outward motion is being questioned in a number of AGN. To investigate this unexpected behavior in more detail and to study the physical emission processes in jets in general and the connection between the central engine and jet launching, is the subject of this PhD project.

 

Contact: PD Dr. Silke Britzen (sbritzen@mpifr-bonn.mpg.de)

 

Site: Bonn, Max-Planck-Institut fr Radioastronomie, VLBI Group

 

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Code: AZ04

Supermassive Binary Black Holes & Merging Galaxies

 

The expected frequent mergers of galaxies over the course of their formation and cosmological evolution must lead to the formation of supermassive binary black holes. Black hole binary mergers could be responsible for many quasars. Detecting more such binary systems is therefore of great interest for key topics in astrophysics ranging from galaxy formation to activity in galaxies. A number of phenomena were attributed to the presence of binary systems, including X-shaped radio galaxies and double-double radio galaxies, precession of a jet emitted by one of the binary components, wiggling of a jet due to the orbital motion, periodic variations in the luminosity due to perturbation of an accretion disk around one of the holes, binary galaxies with radio-jet cores, and binary quasars, etc.

 

Project aims: The research planned for the PhD project focuses on the investigation of the connection between galaxy interactions and active galactic nuclei with particular emphasis on the proof of the existence and analysis of supermassive binary systems in the centers of AGN.

 

Contact: PD Dr. Silke Britzen (sbritzen@mpifr-bonn.mpg.de)

 

Site: Bonn, Max-Planck-Institut fr Radioastronomie, VLBI Group

 

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Code: AZ05

Multi-band study of structural and emission evolution of the quasar 3C273

 

The first quasar discovered, 3C273 remains an archetype object for studies of relativistic flows and physical processes in the vicinity of supermassive black holes in active galaxies (cf., Courvoisier 1998). Since 1970-s, 3C273 has been monitored almost uninterruptedly in all bands, most notably at high- energies with space observatories INTEGRAL and FERMI and at a milliarcsecond resolution in the radio regime with very long baseline interferometry (VLBI). Combining various extended monitoring programs offers undoubtedly the best opportunity to understand the physics of formation and evolution of relativistic flows, and this approach has been applied to observations of 3C273 covering the period through 2000 (Trler et al. 2000). We would like to extend this program to include the latest high-energy and optical observations of 3C273 and combine them with the vast observational database of VLBI observations of the radio emission in this object. This would enable studies of internal structure (cf., Lobanov & Zensus 2001) and spectral evolution (cf., Lobanov & Zensus 1999, Trler et al. 2000) of the flow, and provide the best physical framework for understanding the physical mechanism and location of the production of high-energy emission in AGN.

 

Bibliography:

Courvoisier et al. 1998, A&ARv, 9, 1

Lobanov & Zensus, 1999, ApJ, 521, 509

Lobanov & Zensus, 2001, Science, 294, 128

Trler, Courvoisier & Paltani 2000, A&A, 361, 850

 

Contact: Dr. Andrei Lobanov (alobanov@mpifr-bonn.mpg.de), Prof. Dr. Thierry Courvoisier (thierry.courvoisier@obs.unige.ch)

 

Site: Bonn, Max-Planck-Institut fr Radioastronomie, VLBI Group

 

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Code: AZ06

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

86 GHz VLBI Survey of Ultracompact Radio Emission in Active Galactic Nuclei

 

Very Long Baseline Interferometry (VLBI) Observations at a frequency of 86 GHz (wavelength of 3 mm) reach a resolution of about 50 microarcseconds and enable detailed studies of ultracompact radio emission in active galactic nuclei. Coming from innermost regions of radio jets, this emission reflects processes governing acceleration and collimation of relativistic flows and probes physical conditions in the immediate vicinity of central supermassive black holes on scales down to a few tens of gravitational radii. Systematic studies of radio sources on such scales offer the best opportunity to understand generic properties of relativistic flows and address intricate evolution of individual objects. Founded upon the success of several earlier millimeter VLBI surveys (cf., Lobanov et al. 2001, Lee et al. 2008), this project will benefit from recent improvements in sensitivity and calibration accuracy of the Global Millimeter VLBI Array network. The target sample consists of more than 400 objects, signifying roughly a four time increase in the total number of objects imaged with VLBI at 86 GHz. Combined with data from existing large VLBI surveys at lower frequencies (VLBA, MOJAVE, VCS, and USNO surveys), this project will provide an excellent opportunity to study intricate processes in the vicinity of supermassive black holes, at the earliest stages of formation and evolution of extragalactic relativistic outflows.

 

Bibliography:

Lee, S.S. et al. 2008, AJ, 136, 159 Lobanov, A.P. et al. 2000, A&A, 364, 391

 

Contact: Dr. Andrei Lobanov (alobanov@mpifr-bonn.mpg.de), Dr. Thomas P. Krichbaum (tkrichbaum@mpifr-bonn.mpg.de),  Prof. Dr. Anton Zensus (azensus@mpifr-bonn.mpg.de)

 

Site: Bonn, Max-Planck-Institut fr Radioastronomie, VLBI Group

 

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Code: AZ07

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Localization of non-thermal continuum production in AGN

 

Localizing the sites where non-thermal continuum is produced in AGN is pivotal for understanding their physics. Presently, this localization is largely based on information obtained from observations of the SED and correlated variability of the broad-band continuum emission in AGN. High-resolution radio observations made with Very Long Baseline Interferometry (VLBI) enable in some cases direct spatial localization of the optical, X-ray and Gamma-ray flares in AGN. Correlations observed between parsec-scale radio emission and optical and gamma-ray continuum indicate that a significant fraction of non-thermal continuum may be produced in extended regions of relativistic jet, thus requiring serious rethinking of existing models for the high-energy emission production. The project will be a continuation of our recent efforts in this field (see references). The work will be focussed on further exploration and better understanding of radio-gamma and radio-TeV relations in powerful AGN, using Fermi/LAT and HESS/MAGIC data in combination with extensive VLBI monitoring data from the MOJAVE survey, geodetic VLBI data and new VLBI observations.

 

Bibliography:

Arshakian, Leon-Tavares, Lobanov et al. 2010, MNRAS, 401, 1231

Leon-Tavares, Lobanov, Chavushyan et al. 2010, ApJ, 715, 355

 

Contact: Dr. Andrei Lobanov (alobanov@mpifr-bonn.mpg.de)

Site: Bonn, Max-Planck-Institut fr Radioastronomie, VLBI Group

 

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Code: AZ08

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Jet physics and black hole vicinity at microarcsecond scales

 

Very long baseline interferometry (VLBI) with the space-borne antenna Spektr-R of the Russian-led mission "RadioAstron" provides   an unprecedented angular resolution, reaching down to 10   microarcseconds of arc. This enables studies of jet physics and   black hole vicinity on scales of less than 1000 gravitational   radii, which is a unique opportunity to understand the driving   force behind ultrarelativistic plasma produced in active galactic   nuclei.

 

This project will use the data from dedicated RadioAstron programs   led by the VLBI group (the Key Science Project on imaging of   powerful AGN and the work package on jet acceleration in the   RadioAstron AGN Survey). These data will enable unique studies of   intrinsic evolution of the flow, tracing its acceleration on scales   from a thousand to a million of gravitational radii, and   determining the dominant physical mechanism behind it.

 

Bibliography:

Kardashev, N.S. et al. 2013, Astron. Rep., 57, 153

Lee, S.-S. et al. 2008, AJ, 136, 159

Lobanov, A.P. et al. 2000, A&A, 364, 391

 

Contact:  Dr. Andrei Lobanov (alobanov@mpifr-bonn.mpg.de), Dr. Thomas P. Krichbaum (tkrichbaum@mpifr-bonn.mpg.de),  Prof. Dr. Anton Zensus (azensus@mpifr-bonn.mpg.de)

 

Site: Bonn, Max-Planck-Institut fr Radioastronomie, VLBI Group

 

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Code: AZ09

Relativistic simulations of galactic flows and feedback

 

This project aims to study galaxy feedback by jets by using numerical simulations of relativistic, magnetohydrodynamic flows in supercomputing facilities as a laboratory. The methodology will combine simulations with theoretical studies and comparison with last-generation observations. Jets are a common feature in radio-loud active galaxies. They are formed in a very compact region around a supermassive black hole hosted by the galaxy at its nucleus, and travel along nine orders of magnitude in distance, transporting matter and energy at very high velocity. The interplay between jets, host galaxy and surrounding gas is the top of the list of open questions regarding active galaxy physics. It is possible that the galactic activity and generation of jets completely changes the evolution of the host galaxy, having an important influence on the star-formation rates or the growth of the central black hole, for instance. In order to study the large-scale evolution of jets in a consistent way, it will be necessary to study the jet physics and evolution. At present we are able to use numerical codes in supercomputers, including all the relevant physics of these objects. Given the advent of new generation telescopes, like LOFAR, this project pretends to combine numerical simulations and observations to explain the role of galactic activity in the evolution of galaxies and clusters.

 

Bibliography:

Perucho, Quilis & Mart, Intracluster Medium Reheating by Relativistic Jets, ApJ 743, 42 (2011)

 

Contact: Prof. Dr. Anton Zensus (azensus@mpifr-bonn.mpg.de), Prof. Dr. Eduardo Ros (ros@mpifr-bonn.mpg.de), Dr. Manel Perucho (Univ. Valencia, Spain, perucho@uv.es)

 

Site: Bonn, Max-Planck-Institut fr Radioastronomie, VLBI Group

 

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Code: AZ10

Physics of blazar jets

 

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 have also 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 composition.  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.

 

Bibliography:

Fromm et al., Catching the radio flare in CTA 102. II. VLBI kinematic analysis, A&A 551, A32 (2013)

Fromm et al., Core-shift and spectral analysis of the 2006 radio flare in CTA102, 11th EVN Symp, arXiv:1301.7674 (2013)

 

Contact: Prof. Dr. Anton Zensus (azensus@mpifr-bonn.mpg.de), Prof. Dr. Eduardo Ros (ros@mpifr-bonn.mpg.de), Dr. Manel Perucho (Univ. Valencia, Spain, perucho@uv.es)

 

Site: Bonn, Max-Planck-Institut fr Radioastronomie, VLBI Group

 

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Code: AZ11

Polarisation of AGN jets at the highest resolution

 

VLBI studies of the polarised fine structure of AGN probe the orientation and nature of magnetic fields at the innermost part of their relativistic jets. Present technique, including the enhanced Global Millimetre VLBI Array at 86 GHz, the promise of a phased ALMA at this resolution to be added to the network, and the combination with polarimetric observations with RadioAstron at 22 GHz, are reaching resolutions up to 0.05 milliarcseconds, which hold the key to image in a detail never reached so far.  At 86 GHz, polarimetric observations at 86 GHz are only marginally affected by Faraday rotation and probe the intrinsic linearly polarised emission.  We aim to probe if an oblique shock at the innermost part of the jet is responsible of the observed polarised emission, and the 3D complex structure of the jet close to its nozzle at the highest resolution so far.  The addition of RadioAstron data to the mm-VLBI results and comparing to available 43-GHz VLBI polarised data of prominent blazars will probe the opacity and characterise the spectral behaviour of the jet base, even transversally to it, with the sharpest images ever achieved.

 

Bibliography:

Mart-Vidal, I. et al, On the calibration of full-polarization 86 GHz global VLBI observations, A&A 542, 107 (2012)

Kardashev, N.S. et al, RadioAstron - A telescope with a size of 300 000 km: Main parameters and first observational results, Astron. Rep. 57, 153 (2013)

 

Contact: Prof. Dr. Anton Zensus (azensus@mpifr-bonn.mpg.de), Prof. Dr. Eduardo Ros (ros@mpifr-bonn.mpg.de), Dr. Antxon Alberdi (IAA-CSIC, Granada, Spain, antxon@iaa.es)

 

Site: Bonn, Max-Planck-Institut fr Radioastronomie, VLBI Group

 

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Code: AZ12

Imaging the region around Black Holes and the Origin of Jets

 

A better understanding of the physical processes acting in the ultimate  vicinity of super-massive black holes is needed. Here the  powerful relativistic radio jets are being launched and accelerated and  the observed broad-band variability (radio to TeV) has its physical origin.

 

The angular resolution of an interferometer increases with decreasing wavelength. Very Long Baseline Interferometry at short millimeter wavelength (mm-VLBI)  allows to image compact radio sources with unsurpassed angular and spatial  resolution. Since the source intrinsic opacity is also decreasing with increasing frequency,  mm-VLBI also offers a second advantage: the ability to probe deeper into the self-absorbed regions of AGN, regions which are usually not observable at the longer cm-wavelengths. Therefore mm-VLBI facilitates more detailed studies of the  core regions than ever before.

 

To date mm-VLBI is done at different frequencies (43, 86, 230 GHz) using the available VLBI networks (EVN, VLBA, HSA, GMVA, EHT). While  at the longer wavelengths (43 and 86 GHz) high quality imaging already  is possible, VLBI at 230 GHz is still in a development phase and is more demanding. In next few years, it is expected that ALMA will participate in mm-VLBI. This will dramatically boost the sensitivity, and should lead to new discoveries.

 

Project aims: The main aim of this research project is to image and study Active Galactic Nuclei (Quasars, BLLac Objects, Radio Galaxies, etc.) with highest possible  resolution in the mm-band, addressing questions related to AGN activity, the physical  origin of jets, the details of the jet launching and of the primary acceleration  processes. For this the jet kinematics, their spectral and polarimetric properties  will be studied on spatial scales which are as close as possible to the central engine  (scales of a few 10 - 1000 gravitational radii).

 

For very nearby sources, like the super-massive Black Hole in the center of our galaxy (Sgr A*)  and in the radio galaxy M87 (Virgo A), VLBI imaging at 3mm and 1mm wavelength (86, 230 GHz)  reaches scales of about 4-6 Schwarzschild radii! One (but not the only) focus of this VLBI  project therefore is a continuation of the VLBI study of these sources, aiming at  better radio-images and a more detailed studies of these nearby objects.

 

In this PhD-project, the applicant is supposed to participate in the further development of global mm-VLBI. This includes all steps from the proposing of VLBI experiments, the actual observations, to the final imaging  and the scientific interpretation. The combination of new and archival data provides already a sufficient data base to ensure an immediate start of the  PhD project, which of course should be complemented by new experiments.

 

Further reading:

http://www3.mpifr-bonn.mpg.de/div/vlbi/globalmm/lit.html

 

Contact: Dr. Thomas P. Krichbaum (tkrichbaum@mpifr-bonn.mpg.de), Prof. Dr. Anton Zensus (azensus@mpifr-bonn.mpg.de)

 

Site: Bonn, Max-Planck-Institut fr Radioastronomie, VLBI Group

 

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Code: AZ13

Fermi-GST Multi-frequency Monitoring Alliance (F-GAMMA): AGN astrophysics in the Fermi-GST era

 

Unlike the normal galaxies where the observed radiation is simply the sum of mostly the light produced by their stellar population, Active Galactic Nuclei appear to radiate inconceivable amounts of energy from a very small - compact - nuclear region. These extraordinary systems are believed to be powered by a Super Massive black hole (~106 Msun) hosted by their galactic center. Matter is accreted through a candescent accretion disk surrounding the black hole and then it is shotted ionized into relativistic plasma jets perpendicularly to that disk. The plasma jets emit primarily via synchrotron mechanism which is consequently involved in several secondary process such as Inverse Compton scattering.

 

This simple, at first glance, configuration is creating an enormous variety of phenomenologies blended in a whole zoo with families, classes and sub-classes. The plasma jets can reach distances of kpc to Mpc while the involved relativistic velocities induce effects unseen in other systems. The enormous magnitude and complexity of these systems and the plurality of their constituents not only intrigues our need to understand the complicated emission processes but also gives AGNs the first role in the cosmic scene. Their jets for instance is believed the regulate the activity in members of clusters of galaxies while the claimed relation between the AGN activity as a stage in the interaction of galaxies allows the study of extreme gravitational fields.

 

Despite the decades of research the exact processes at play are intensely debated. What mechanisms produce the jets, how are the particles accelerated, what is the role of the magnetic fields, how exactly is the radiation produced and what is the location of the high energy emission, how is the jet activity influencing the environment, are only some indicative questions to be addressed among a series of astrophysical problems to be attacked. Among all the classes of AGNs, blazars are characterized by very small viewing angles to the jet axis. This implies extreme characteristics, such as: extremely broad-band emission, intense variability, large degree of polarization and intense polarization variability, highly superluminal speeds and many more. Consequently they are unique probes of the AGN physics. simultaneous multi-frequency studies of blazars hold a great potential in AGN research. The gamma- ray satellite Fermi-GST launched in summer 2008 has revolutionized this field by providing several daily scans of the entire gamma-ray sky allowing for the first time ever really simultaneous studies.

 

In January 2007 the VLBI group of the MPIfR formed a scientific alliance between several state-of-the- art facilities (F-GAMMA program) in order to conduct coordinated multi-frequency studies of selected blazars in collaboration with the Fermi-GST satellite. The main facilities are: the 100-m telescope in Germany, the 30-m IRAM telescope in Spain and the APEX telescope in Chile. Additionally, we have developed an extended network of collaborators such as the 40-m OVRO telescope in California, the 1,2 m optical telescope in Crete, the MOJAVE VLBA survey team, the AGN group of the university of Perugia and others. Currently, the F-GAMMA team consists of four scientists and 2 students and it is ever growing.

 

After 6.5 years of the program there is an immense volume of high quality data ready to be analyzed. The team has a broadest approach to blazar physics and is involved in all possible directions such as, emission mechanisms, population studies, spectral energy distribution studies, variability studies, VLBI blazar studies, cross-band polarization studies, gamma-ray and radio correlations etc. Potential students will have the opportunity to choose from a variety of topics. They will be encouraged and guided to write proposals for and travel to observing facilities in the world, to travel to schools and conferences and to gain broad experience in observing techniques.

 

 

Contact: Dr. Emmanouil Angelakis (eangelakis@mpifr-bonn.mpg.de), Dr. Lars Fuhrmann (lfuhrmann@mpifr-bonn.mpg.de), Prof. Dr. J. Anton Zensus (azensus@mpifr-bonn.mpg.de)

Site: Bonn, Max-Planck-Institut fr Radioastronomie, VLBI Group

 

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Code: AZ14

Physics of Blazars with State-of-the-art Optical Polarimetry

 

Blazars are the most active galaxies known. They are powered by relativistic jets of matter speeding towards us almost head-on at the speed of light, radiating exclusively through extreme, non-thermal particle interactions, energized by accretion onto supermassive black holes. Despite intensive observational and theoretical efforts over the last four decades, the details of blazar astrophysics remain elusive. The launch of NASAs Fermi Gamma-ray Space Telescope in 2008 has provided an unprecedented opportunity for the systematic study of blazar jets and has prompted large-scale blazar monitoring efforts across wavelengths.

 

In such a multi-wavelength campaign, a novel effect was discovered: fast changes in the optical polarization during gamma-ray flares. Such events probe the magnetic field structure in the jet and the evolution of disturbances responsible for blazar flares. Their systematic study can answer long-standing questions in our theoretical understanding of jets; however, current optical polarimetry programs are not adequate to find and follow similar events with the efficiency and time-resolution needed.

 

RoboPol is a massive program of optical polarimetric monitoring of over 100 blazars, using a specially-built, innovative polarimeter mounted on the 1.3 m telescope of the University of Cretes Skinakas Observatory, a dynamical observing schedule, and a large amount of dedicated telescope time. The program is a collaboration between the Max-Planck Institute for Radioastronomy, the University of Crete and the Foundation for Research and Technology - Hellas in Greece, Caltech in the US, the Nicolaus Copernicus University in Poland, and the Inter-University Centre for Astronomy and Astrophysics in India.

 

The PhD student will collaborate closely with RoboPol members in MPIfR (coordinated by E. Angelakis) and the U. of Crete (coordinated by V. Pavlidou), as well as the other international RoboPol collaborators. The student will have the opportunity to combine polarization observations with datasets across wavelengths, and participate in a complementary theory and phenomenology program, aiming to constrain the underlying physics of the blazar phenomenon.

 

Contact:   Prof. V. Pavlidou (pavlidou@physics.uoc.gr),  Prof. Dr. J. Anton Zensus (azensus@mpifr-bonn.mpg.de), Dr. Emmanouil Angelakis (eangelakis@mpifr-bonn.mpg.de)

Site: Bonn, Max-Planck-Institut fr Radioastronomie, VLBI Group

 

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Millimeter and Sub-millimeter Group

Director: Prof. Dr. Karl Menten

 

Group website

 

 

Code: KM01

The Megamaser Cosmology Project

 

Dark Energy (DE) accounts for 73% of the energy density of the   universe, dominates its present expansion, and determines its ultimate fate. Understanding DE may be the most important problem in fundamental physics today. The Cosmic Microwave Background (CMB) on its own cannot provide a high precision estimate on DE's equation of state. To constrain the nature of DE, the best complement to CMB data is a measurement of the  Hubble constant (Ho) to better than 3%. 

 

A particularly promising path to measure Ho to such high  precision involves direct geometric distance determinations of circumnuclear water masers in galaxies in the Hubble flow, at distances of 50-200 Mpc. The Megamaser Cosmology Project (MCP) is an ambitious project to achieve this goal. Luminous water vapor masers, as they move on Keplerian orbits around  supermassive black holes, are observed at high spatial  resolution, using the tools of Very Long Baseline Interferometry (VLBI). Aside of distances, the measurements also allow for accurate mass determinations of the central engines and provide first maps of the shape and morphology of the circumnuclear disks of active galaxies.

 

Bibliography:

C.Y. Kuo et al. 2011, Astrophy. Journal 727, 20

J.E. Greene et al. 2010, Astrophys. Journal 721, 26

J.A. Braatz et al. 2010, Astrophys. Journal 718, 657

M. Reid et al. 2009, Astrophysical Journal 695, 287

C.M.V. Impellizzeri et al. 2008, Nature 456, 927

F.Y. Lo 2005, Ann. Rev. Astron. & AStrophys. 43, 625

C. Henkel et al. 2005, Astrophys. & Space Science 295, 107

 

Contact: Dr. C. Henkel (chenkel@mpifr-bonn.mpg.de), Prof. Dr. Matthias Kadler (matthias.kadler@astro.uni-wuerzburg.de), Dr. A. Roy, Dr. J. Braatz

 

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

 

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Code: KM02

Complex organic chemistry in the interstellar medium

 

About 180 molecules have been detected in the interstellar medium (ISM) or in  circumstellar envelopes so far. About one third of them contain 6 atoms or  more and are called "complex" molecules. All these complex molecules are  organic. The search for complex organic molecules (COMs) in the ISM is in part  motivated by the discovery of more than 80 distinct amino acids in meteorites  fallen on Earth as well as the recent detection of glycine, the simplest amino  acid, in samples returned from a comet to Earth by the Stardust mission. These  discoveries strongly suggest that interstellar chemistry is capable of  producing such COMs, which could be widespread in our Galaxy. However, even  glycine has not be detected in the ISM so far.

 

Sagittarius B2 (Sgr B2) is the most massive star-forming region in our Galaxy.  It contains two massive clumps (N and M) which host clusters of compact H II  regions. Many COMs were first detected toward Sgr B2(N) thanks to its immense  hydrogen column density. This source has turned out to be one of the best  interstellar hunting grounds for COMs. A few years ago, we carried out a  complete spectral survey of both N and M at 3mm with the IRAM 30m single-dish  radiotelescope. This extensive survey led to the detection of several new COMs  and provided an inventory of the molecular content of N and M. To make further  progress in extending the inventory of COMs in Sgr B2 and derive tighter  constraints on their location, origin, and abundance, we are currently  performing a similar spectral survey with the recently built Atacama Large  Millimeter/submillimeter Array (ALMA). This international facility is  currently the most powerful interferometer in the mm/submm wavelength range.  We expect an improvement in both angular resolution and sensitivity by more  than one order of magnitude compared to our previous single-dish survey of  Sgr B2.

 

Project aims:

The PhD project will focus on the analysis and interpretation of our ALMA  spectral survey of Sgr B2. The aim is to derive the abundance and location of  the detected molecules in order to test predictions of state-of-the-art  chemical models and set constraints on the evolutionary stage of the sources  detected in the field of view. A close collaboration with Dr. Robin Garrod  (Cornell University), who is developing state-of-the-art chemical models, is  expected.

 

Bibliography:

Belloche et al. 2008, A&A, 482, 179

Belloche et al. 2009, A&A, 499, 215

Garrod 2013, ApJ, 765, 60

Herbst & van Dishoeck 2009, ARA&A, 47, 427

 

Contact: Arnaud Belloche (belloche@mpifr-bonn.mpg.de), Prof. Dr. Karl Menten (kmenten@mpifr-bonn.mpg.de)

 

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

 

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Code: KM03

Square degree mapping of giant star forming complexes at 350 micron

 

The APEX Telescope Large Area Survey of the Galaxy (ATLASGAL), which has just been completed, reveals 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 on the degree scale. Little is known about the properties of the cold interstellar medium on such large scales, such as dust emissivity and temperatures. When combining the A-MKID data with the Herschel/Hi-GAL survey at 60 to 600 micron, it will be possible to:

 

Project aims:

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

 

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

 

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

 

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Code: KM04

Molecular excitation and abundances through the evolution of massive star forming regions

 

The just finished ATLASGAL project conducted an unbiased survey of the inner Galactic disk using the APEX telescope. One of the major goals is to reveal objects associated with massive star formation at various stages, to study their timescales and their distribution in the inner Galaxy. With a large field of view of 11 arcmin, and a resolution of 18" at 870 micron, the MPIfR-built bolometer array LABOCA is the perfect tool to conduct such a large scale survey in a limited amount of time. This instrument allows, both, to resolve sources of 0.1 pc size within 1 kpc, and to map the dust component in the interstellar medium on large scales little explored so far.

 

Spectral line follow-ups of newly identified massive star forming clumps have been conducted at 3mm with the Mopra and IRAM 30m telescope and at 870micrion with the APEX FLASH receiver. The prime goals using these data are:

 

Project aims:

virial masses of the clumps will be derived from line width measurements

the kinematical signatures of outflows and infall will be studied

density and temperatures will be measured with various molecules and

  detailed excitation modeling

the chemical evolution will be studied by measuring molecular

  abundances and comparing them with chemical models

 

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

 

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

 

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Code: KM05

Probing the inner workings of massive star forming regions

 

The just finished ATLASGAL project conducted an unbiased survey of the inner Galactic disk using the APEX telescope. One of the major goals is to reveal objects associated with massive star formation at various stages, to study their timescales and their distribution in the inner Galaxy. With a large field of view of 11 arcmin, and a resolution of 18" at 870 micron, the MPIfR-built bolometer array LABOCA is the perfect tool to conduct such a large scale survey in a limited amount of time. This instrument allows, both, to resolve sources of 0.1 pc size within 1 kpc, and to map the dust component in the interstellar medium on large scales little explored so far.

 

The logical next step in the analysis of the newly found massive star forming regions is to conduct high angular resolution interferometer follow ups of a representative and well-chosen subsample to investigate the evolutionary sequence and inner workings of massive star forming regions. With ALMA now being the most powerful mm/submm

interferometer, it will be used for these follow ups. The prime goals are:

 

Project aims:

to investigate the details of the fragmentation process.

to study outflows in massive star forming regions.

to search for disks around massive (proto) stars

to study the physical and chemical conditions close to the forming stars.

 

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

 

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

 

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Code: KM06

A comprehensive Galactic plane radio wavelength star formation survey

 

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 fr Radioastronomie, Millimeter and Submillimeter Astronomy Group

 

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Code: KM07

Massive molecular outflows

 

The detailed physical processes at the origin of high-mass stars (here defined as ionizing OB stars; i.e., earlier than B3 or M*> 8 M_sol) are still to be fully recognized and understood. Whether they form through a scaled-up version of the low-mass star formation process or by means of a specific process is still an open issue. Observations seem to contradict both scenarios as the level of turbulence in massive dense cores is not enough for the first scenario nor the level of fragmentation is as high as predicted by alternative models.

 

Important insides in the mechanisms that lead to the formation of massive stars may come from observations of a large statical sample of deeply embedded massive young stellar objects (YSOs) aimed at characterising how they accrete material from their surrounding envelopes. While in principle detection of circumstellar disks is the ultimate test to verify whether massive star formation is a scaled-up version of low-mass star formation, circumstellar disks are still a challenge for observations given the average distance of massive YSOs and their high level of multiplicity. On the other hand, jets and outflows are a direct consequence of accretion onto the protostar,  they have linear sizes much larger than those of disks and are  associated with emission from some molecules such as SiO that are  associated unambiguously only  with shocks.

 

Project aims:

The PhD project will focus on the analysis and interpretation of existing Herschel water data complemented by observations (CO, SiO etc) with the APEX telescope. High angular resolution observations to study multiplicity in the sources and resolve single outflows will also be collected.

The aim is to derive properties of massive molecular outflows (collimation, physics and energetics) in a statical sample of sources and compare with the same properties of molecular outflows from low-mass YSOs to verify whether massive molecular outflows are a scaled-up version of their low-mass counterparts or wether their properties change at a given mass and luminosity of the central object.

 

Bibliography:

Arce et al. 2007, Protostars and Planets V, 245

Bontemps et al. 2010, A&A, 524, A18

Cesaroni et al 2007, Protostars and Planets V, 197

Leurini et al 2013, A&A, 554, A35

 

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

 

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

 

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Code: KM08

Magnetized turbulence in star forming regions

 

keywords: star formation, magnetic fields, turbulence, spectroscopy, astrochemistry, chemical modelling, single-dish observations.

 

Magnetic fields and turbulence are the most debated agents that regulate the process of star formation. Dense cores within clouds can collapse once the turbulence is dissipated and magnetic fields are no longer frozen in the gas. An observational project based on spectroscopy techniques is proposed  to investigate the interplay between turbulence  and magnetic fields and their effect on the onset of star formation. In this project, the turbulent ambipolar diffusion scale, i.e., the spatial wavelength at which ion and neutral species decouple and turbulent energy dissipates, is determined in star forming clouds. This parameter will provide an estimate for the magnetic field strength. This can be achieved by comparing the line-widths of the spectra of coexistent ion and neutral molecular species such as HCO+/HCN and H13CO+/H13CN pairs. The project is broken down to the following tasks, which are aimed at annual achievements and publications:

 

   Analysis of a rich set of available data of intensity maps of two different transitions of each of the HCN/HCO+ and H13CN/H13CO+ pairs in the Serpens South Cluster, an active star forming site in the Aquila rift, obtained with the JCMT and APEX telescopes. The turbulent ambipolar diffusion scale and magnetic field strength calculated from this analysis can be used to estimate the rate of transfer of turbulent energy, and in combination with the dust polarization map already obtained with the PolKa polarimeter at APEX will provide a more accurate picture of the magnetic field in this source.

   Expanding this method to new molecular pairs such as the NO+/NO pair in protostellar cores containing warm gas, and also the HCO+/CO pair in cold pre-stellar cores. Observations will be carried out with the APEX telescope.

   Adding the effect of turbulence cascade and dissipation to an available chemical model to obtain a more realistic evolution trend for the ion and neutral pairs, as observed in turbulent clouds. 

 

Bibliography:

Li, H., & Houde, M. 2008, ApJ, 677, 1151

Hezareh, T., Houde, M., McCoey, C., & Li, H-B. 2010, ApJ, 720, 603

Tassis, K., Hezareh, T., & Willacy, K. 2012, ApJ, 760, 57 

 

Contact:  Dr. Talayeh Hezareh (thezareh@mpifr-bonn.mpg.de), Prof. Dr. Karl Menten (kmenten@mpifr-bonn.mpg.de)

 

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

 

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Fundamental Physics in Radio Astronomy Group

Director: Prof. Dr. Michael Kramer

 

Group website

 

 

Code: MK01

Monitoring the Interstellar Weather with Pulsars

 

Our Galaxy is a dynamical and constantly evolving system. The interstellar medium (ISM) appears constant at large scales (~kpc) but is turbulent at small scales (~pc). These changes impact on many of the observed properties of astronomical objects but rarely does one have the opportunity to monitor those changes as accurately as with pulsars. The amount of pulse dispersion by the ISM across our observing band is given by the Dispersion Measure (DM), which is equal to the integrated amount of interstellar matter between the pulsar and the observer. The wide observing bands of modern instruments and the low observing frequencies attainable with telescopes like LOFAR conspire towards very accurately measured dispersion delays and, hence, DMs. Also, the pulsed emission from pulsars is highly polarised and the magnetic field of the ISM causes the plane of polarisation to rotate as those pulses travel through the Galaxy. The integrated amount of this rotation is expressed with the Rotation Measure (RM) and, again, can be measured with great accuracy across wide frequency bands. Both DM and RM should remain constant with time in a static system but are constantly changing in the dynamical Milky Way. Using a high number of bright, polarised pulsars we can closely track those changes and interpret them as changes of the matter distribution in the Galaxy and changes in the Galactic Magnetic field.

 

The LOFAR station at Effelsberg as well as the 100m Effelsberg single-dish radio telescope will provide excellent frequency coverage from several GHz to tens of MHz, thus providing the means to monitor pulsar DMs and RMs with unprecedented accuracy. Both instruments incorporate very large bandwidths, with LOFAR having 96 MHz at 150 MHz (high band) and 50 MHz (low band), and Effelsberg reaching up to 3 GHz of bandwidth at ~ 1 GHz, with the newly installed Ultra-Broad-Band (UBB) receiver. The telescopes will be easily accessible from MPIfR and are expected to generate a large amount of total-flux and polarisation data from regularly monitored pulsars, which will be analysed by the project's investigators.

 

The project will be conducted within the Fundamental Physics in Radio Astronomy group of the MPIfR lead by Prof. Michael Kramer. His team's research concentrates on various aspects of fundamental physics, namely here 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".

 

Contact: ,  Dr. Aristeidis Noutsos (anoutsos@mpifr-bonn.mpg.de) , Prof. Dr. Michael Kramer (mkramer@mpifr-bonn.mpg.de)

 

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

 

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Code: MK02

Searching the Galaxy for pulsars

 

 The largest telescopes in the world are currently undertaking surveys to search for pulsars. The group in Bonn is leading surveys using the 64-m Parkes telescope in Australia and our 100-m Effelsberg telescope near Bonn. Their locations allow these telescopes cover the whole sky. Although nearly 2000 pulsars have been discovered  it is the most unusual pulsars that really push forward research areas such as, general relativity, pulsar evolution and emission mechanisms. In addition to using large telescopes these new surveys use cutting edge hardware. New receivers and a new generation of data recording 'backends' have increased the sensitivity of these surveys dramatically over previous efforts, allowing us to search deep into the Galaxy for the periodic pulsar signals.

 

The successful applicant would take part in the observations and data taking. They would be involved in the processing using powerful computer clusters (in Bonn and at partner institutions) including using Einstein@Home from the AEI (similar to SETI@Home). Finally they would be expected to lead the follow up observations and analysis of interesting discoveries.

 

The project will be conducted within the Fundamental Physics in Radio Astronomy group of the MPIfR lead by Prof. Michael Kramer. His team's research 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.

 

Contact: ,  Dr. David Champion(davidjohnchampion@gmail.com) , Prof. Dr. Michael Kramer (mkramer@mpifr-bonn.mpg.de)

 

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

 

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Code: MK03

Probing Pulsars and their Environments

 

High-precision timing of pulsars enables a host of detailed investigations into the pulsars' characteristics, their binary companions; and the interstellar medium that pervades the Milky Way. These investigations can now be performed at unprecedented precision with new observing hardware in the form of low-frequency LOFAR antennas placed across Germany and Europe; and the newly built ultra-broad-band receiver on the Effelsberg 100-m radio telescope.

 

In this project, the student will have the opportunity to study different binary systems with these new observing systems. Specific examples include the so-called "black widow" pulsars, which are in very close and eclipsing orbits with stellar companions that are being destroyed by the energetic pulsar wind and strong gravitational pull. These systems can be used to investigate the internal structure of the companion stars; their stellar wind properties; and the accretion process that is predicted to accelerate pulsar spin. A second population are the pulsars in orbit around other neutron stars, which can be used to investigate relativistic effects like geodetic precession and gravitational-wave emission. Furthermore, all pulsars can be used to probe the interstellar medium between us and the pulsars; and to investigate how variations in this medium could corrupt all ongoing high-precision timing experiments.

 

The successful candidate will lead pulsar timing investigations of eclipsing and binary pulsars with various LOFAR stations and with the new ultra-broad-band receiver on the Effelsberg 100-m telescope, which is the most sensitive observing system ever constructed for observations at these frequencies. Affinity with radio astronomy techniques and programming is a plus.

 

This project will be conducted within the Fundamental Physics in Radio Astronomy group of the MPIfR, lead by Prof. Michael Kramer; and in close collaboration with the Radio Astronomy group of Prof. Joris Verbiest at the University of Bielefeld; the candidate will be expected to split his/her time between these two institutions.

 

Contact: Prof. Dr. Joris Verbiest (verbiest@physik.uni-bielefeld.de), Prof. Dr. Michael Kramer (mkramer@mpifr.de)

 

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

 

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Code: MK04

Advanced interferometry techniques

 

The technique of interferometry is essential to reach high resolutions in radio astronomy. Progress in building new radio interferometers is fast, and a number of SKA pathfinder instruments are becoming available now. The development of improved data analysis and imaging techniques is lagging behind even though new ideas are essential to optimise the use of the new instruments. We offer a variety of possible projects in this field, e.g. (a) New imaging techniques based on sparse reconstruction and compressive sensing with possible science applications in gravitational lensing and other fields. (b) Development of analysis techniques for high-resolution observations with LOFAR using the international baselines. (c) Utilising interstellar scattering disks as huge interferometers with incredibly high resolution but the need of highly sophisticated analysis techniques, e.g. to resolve emission regions on pulsars. (d) Exploring new routes for intensity interferometry at optical and potentially shorter wavelengths to reach the highest resolutions for limited types of sources.

 

Contact: Dr. Olaf Wucknitz (wucknitz@mpifr-bonn.mpg.de), Prof. Dr. Michael Kramer (mkramer@mpifr-bonn.mpg.de)

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

 

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Code: MK05

Mapping magnetic fields in supergiant shells

 

In the interstellar medium of galaxies, supergiant shells heat and compress ambient gas to shape galactic disks. They are also likely an efficient agent in the generation of galactic-scale magnetic fields. In order to understand the role of supergiant shells in the interstellar medium on a global scale, measurements of their magnetic fields are much needed and long overdue. Our neighboring galaxy, the Large Magellanic Cloud, offers an excellent laboratory to carry out such a study.

 

The successful applicant will process wide-band radio interferometric data of the diffuse polarized synchrotron emission from supergiant shells in the Large Magellanic Cloud. They will be expected to model the magnetic field structures in supergiant shells using techniques such as Faraday tomography. Furthermore, they will perform a detailed comparison of the observed polarized emission with synthetic polarization maps obtained from magneto-hydrodynamic simulations of the turbulent interstellar medium. Spectral line data taken simultaneously with the continuum observations will allow one to investigate the HI-to-CO ratio in supergiant shells, as well as performing a search for Hydroxyl masers.

 

Contact: Prof. Dr. Michael Kramer (mkramer@mpifr-bonn.mpg.de), Dr. Ann Mao (mao@astro.wisc.edu)

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

 

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Code: MK06

A deep line survey with the new ultra-broadband 100-m telescope K-band receiver

 

The Effelsberg 100-m telescope will soon be equipped with a next-generation 1.3-cm receiver (K-band) providing an enormous instantaneous bandwidth of 8 GHz and up to almost 2 million spectral channels. This new instrument is the first of a series of new receivers to make the 100-m telescope fit for the coming decades.

 

The huge bandwidth and high spectral resolution make it possible to observe dozens of interesting molecules in one go, and to potentially detect new lines as well. One of the first projects will be a deep survey for emission lines on various star forming regions.

 

For this survey, 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 as well in analyzing the wealth of data afterwards. A strong background in software engineering is required. Experience with data reduction of radio astronomical data would be a plus.

 

Contact: Dr. Benjamin Winkel (bwinkel@mpifr.de), Dr. A. Kraus (akraus@mpifr.de) Prof. Dr. Michael Kramer (mkramer@mpifr-bonn.mpg.de)

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

 

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University of Bonn

Argelander Institute for Astronomy

 

Group website

 

 

Code: UB01

Common Envelope Evolution

 

Most of the stars in our Galaxy are gravitationally coupled with a close companion in a binary star system. Because stars expand as they age, many in binaries interact by transferring of matter from one star to the other. Often this mass transfer runs out of control and, when the material cannot be accreted onto the companion star, a common envelope forms around both stars. The common envelope is either ejected or becomes the envelope of a new, merged star. This is one of the most important -- but least understood -- phenomena in stellar astrophysics. To understand the outcome of common-envelope evolution is critical to many branches of stellar astrophysics. For example, close white dwarf binaries which may explode as Type Ia supernovae, the standard candles of cosmology, can only form from common envelope ejection. Other related phenomena include novae and the beautiful planetary nebulae.

 

For the first time, a full theoretical prediction of the outcome of common-envelope evolution is possible and this is the aim of the project. State-of-the-art 3D hydrodynamical simulations will be used to construct a model of common-envelope evolution in a stellar evolution code. This approach has many advantages: the initial conditions for mass transfer are modelled correctly, the stellar evolution can be followed indefinitely including accurate energy-transfer and mixing physics, and binary stars across the whole parameter space can be simulated. This project has the potential to be a major breakthrough with ramifications in many fields of astronomy, including the formation of exotic stars (e.g. Wolf-Rayet stars), stellar explosions (type Ia/b/c supernovae and novae) and double white dwarf binaries. These are exciting times for stellar astrophysics in Bonn: the expert help required to carry out such an ambitious project is available in one place for the first time.

 

Contact: ,  Robert Izzard (izzard@astro.uni-bonn.de), Prof. Dr. Michael Kramer (mkramer@mpifr.de)

 

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

 

Reading: http://www.astro.uni-bonn.de/~izzard/doc/papers/2011/comenv_2011-Izzard.pdf

 

Project funding pending: please contact Robert Izzard to determine current status.

 

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Code: UB02

The Stellar Initial Mass Function

 

Investigate (theoretically) how unresolved multiple stellar systems affect an observed mass or luminosity function of stars, and extract the true underlying mass distribution. The full-scale modelling of Galactic-field populations requires treatment of ages, stellar evolution, metallicity distributions and multiplicity of stars as well as Galactic structure. The shape of the IMF below the hydrogen burning mass limit remains uncertain with the possibility of a discontinuity near the stellar/sub-stellar transition region. This is to be studied theoretically using available observational data.

 

Contact: Prof. Dr. Pavel Kroupa (pavel@astro.uni-bonn.de), Prof. Dr. Karl Menten (kmenten@mpifr- bonn.mpg.de)

 

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

 

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Code: UB03

The dynamical evolution of young and old star clusters

 

Star clusters are known to be the fundamental building blocks of galaxies as most stars form in clusters. The physical processes driving early cluster evolution are to be studied with the aim of increasing our understanding of the formation and survival of clusters and the impact on the morphology of entire galaxies of these processes. Theoretical and computational methods will be used to investigate the physics of internal cluster evolution as a result of binary-star activity, stellar evolution and gas expulsion. External influences resulting from time-varying tidal fields of various strengths are to be studied with the aim of better understanding the observed cluster radius-age data including the outer reaches of the Milky Way and in extragalactic systems.

 

Contact: Prof. Dr. Pavel Kroupa (pavel@astro.uni-bonn.de), Prof. Dr. Karl Menten (kmenten@mpifr- bonn.mpg.de)

 

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

 

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Code: UB04

The mass function of star clusters

 

The physical processes leading to early and old cluster evolution influence the observable mass distribution of star clusters. This is to be studied using semi-analytical and numerical methods in order to map-out the dependency of the cluster mass function on the host environment.

 

Contact: Prof. Dr. Pavel Kroupa (pavel@astro.uni-bonn.de)

 

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

 

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Code: UB05

Dwarf galaxies and dark matter

 

Fundamental physical principles (energy and angular-momentum conservation) imply that during early cosmological times when gas-rich pre-galactic rotationally supported structures merged to form the present-day galaxies, tidal tails were expelled and locally fragmented to form tidal-dwarf galaxies (TDGs). Cosmological arguments suggest this population of non-traditional dwarfs to be possibly very significant and that it may dominate the low-luminosity end of the galaxy luminosity function. These TDGs would not contain dark matter and may thus pose a major "contaminant" of the classical or cosmological galaxy population. The dynamical evolution of TDGs in host potentials is to be studied numerically and semi-analytically with the special attention on the Milky-Way satellite population to see if any of the satellites may be ancient TDGs.

 

Contact: Prof. Dr. Pavel Kroupa (pavel@astro.uni-bonn.de)

 

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

 

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Code: UB06

The dynamical evolution of the brown-dwarf population in star forming regions

 

Recent work suggests that brown dwarfs form together with stars but that they follow a different mass distribution which is disjoint from the stellar initial mass function. The fraction of binary systems among brown dwarfs (15 per cent) is also much lower than for stars (50 per cent or more), and their binding energy distributions are very different such that the brown dwarf binaries have an energy truncation at a higher level than stars. This project aims to bring this evidence together to investigate various formation mechanisms of brown dwarfs, and to study theoretically how they disperse throughout their birth cluster comparing their binary, spatial and kinematical properties with those of stars. The work will be performed with the GPU-based supercomputing platforms stationed at the Argelander-Institut and with dedicated codes.

 

Contact: Prof. Dr. Pavel Kroupa (pavel@astro.uni-bonn.de), Prof. Dr. Karl Menten (kmenten@mpifr- bonn.mpg.de)

 

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

 

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Code: UB07

The star-formation rates of dwarf galaxies and the origin of matter

 

Recent work in Bonn has been showing that dwarf galaxies appear to have the same short (3 Gyr) gas- consumption timescales as major galaxies. The aim of this project is to extend this finding to spectro- photometric modeling of dwarf galaxies and to study the possible origin of the matter that must be replenishing the star-forming material.

 

Contact: Prof. Dr. Pavel Kroupa (pavel@astro.uni-bonn.de)

 

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

 

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Code: UB08

Development and testing of a new cosmological model

 

Assuming energy conservation to be valid on a cosmological scale, a new cosmological model can be derived which leads to good agreement with the SNIa data and other recent observational findings such as the star formation behaviour of galaxies of different mass. In this project, the student will work on the growth of structure in this new cosmology and further tests of it.

 

Contact: Prof. Dr. Pavel Kroupa (pavel@astro.uni-bonn.de)

 

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

 

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Code: UB09

Pair-instability supernovae in the local universe

 

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

 

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Code: UB10

Physics of galaxy clusters from SZ and X-ray data

 

Understanding the physical properties of the hot, ionized intra-cluster medium (ICM) is a central theme of galaxy clusters cosmology. The ICM mass and temperature relates to the total gravitational mass of the dark matter in clusters, and morphological features like shock fronts show how clusters are assembled. The ICM is typically observed through its X-ray emission or the Sunyaev-Zel'dovich (SZ) effect, but a combination of these two data provides an even more powerful technique to analyze the cluster properties. The APEX-SZ team at the University of Bonn is actively involved in this field of which the prospective student will become a member. The preliminary task will be to analyze some data taken from the APEX-SZ experiment and compare it available X-ray and optical data. The central theme of this project will be to develop a model independent method for studying cluster morphology, based on APEX-SZ, Planck SZ and X-ray data. This project will also prepare the student for future high-resolution SZ observation and analysis using the CCAT telescope, which will start operating in the year 2017 and for which Bonn University will have access through guaranteed time.

 

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

 

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

 

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Code: UB11

The mystery of galaxy cluster radio halos

 

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.

 

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

 

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

 

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Code: UB12

Panoramic and detailed millimeter-radio views onto the cosmic history of star formation

 

Among the most pressing questions in modern galaxy evolution studies is how stellar mass assembled over cosmic time. Our current understanding of the main drivers of star formation within galaxies is still sparse but over the last years a picture emerged in which the build-up of new stars is tightly connected to the existing stellar mass (e.g. Karim et al. 2011 and references therein). This possibly suggests that simple self-regulated gas-exchange of galaxies and their respective haloes is capable of describing the very localized and highly inefficient process of star formation using only a few parameters (Lilly et al. 2013). Given the highly hierarchical, violent assembly of the large scale dark matter component of the Universe this link is surprising and awaits detailed observational confirmation. Similarly, it has been suggested that  the effects different galaxy environments cause are fully separable with respect to the star formation-mass link (e.g. Peng et al. 2011), a conclusion that clearly awaits observational confirmation at earlier cosmic epochs than probed so far.  

 

High angular resolution radio continuum observations of cosmological deep fields can play an important role in dissecting all these effects and shed light on the related open questions. Radio observations have been highly successful in providing tight constraints for our understanding of star formation over large cosmic timescales (e.g. Karim et al. 2011). The PhD project suggested here will make use of the unique data sets currently observed at the Jansky-VLA in the 2 square degree COSMOS deep field (see Schinnerer et al. 2010 for earlier COSMOS radio observations using the VLA). The angular resolution achieved in this survey will allow us to explore the extent of the star forming regions within galaxies and help to dissect them from the active nuclear regions. Particularly, recently obtained detailed environmental information in the COSMOS field will allow to study the link of star formation and mass in a wide range of galaxy environments, such as clusters, groups and filaments of the large-scale matter distribution in unprecedented detail.  The successful candidate will also have the opportunity to use the radio data in combination with newly obtained mm-data (from single-dish as well as interferometric observations, partially from ALMA) to study star formation at very high redshifts z>4 and to explore further research avenues within the vast panchromatic COSMOS survey data sets. Alexander Karim and Frank Bertoldi are full members of the international COSMOS consortium and have access to all the latest deep observations from a large variety of instruments. Critically, they play leading roles in the ongoing field observations using the expanded Very Large Array (Jansky-VLA; USA) as well as the 2mm GISMO bolometer array operating at the IRAM 30m telescope on Pico Veleta (Spain).

 

Bibliography

Karim et al. 2011, ApJ, 730, 61

Lilly et al. 2013, ApJ (in press.), arXiv:1303.5059

Peng et al. 2010, ApJ, 721, 93

Schinnerer et al. 2010, ApJS, 188, 384

 

Contact: Prof. Dr. Frank Bertoldi (bertoldi@astro.uni-bonn.de),  Dr. Alexander Karim (karim@astro.uni-bonn.de), Dr. Benjamin Magnelli (magnelli@astro.uni-bonn.de)

 

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

                                    

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Code: UB13

Submillimeter observations of the highest redshift galaxies and quasars

 

The wider scientific aim of the PhD project is to characterize the physical properties and structure of the high–redshift star forming galaxies   through dedicated observations of dust continuum emission and of molecular  and atomic fine structure lines. We will thereby try to establish a coherent picture of the conditions for star formation in starburst galaxies, primarily in star-forming galaxies during the early epoch of galaxy formation, when most of the stars ever formed were born.  We investigate, e.g., the relation between the gas and star formation properties to constrain the effects of feedback on the assembly and evolution of galaxies. The PhD projects will optimally embark on new  observational capabilities of the upgraded IRAM Plateau de Bure interferometer, the Expanded VLA,  the ALMA observatory, and eventually of CCAT. The PhD student will analyze and exploit our already available and to be observed data  and motivate and prepare new observations with these facilities.

 

Closely working within a successful, small international collaboration (F.Walter, C.Carilli, A.Omont, R.Wang, V.Smolcic, X.Fan and others), we will investigate the physical, chemical and dynamical conditions of the star forming gas in high redshift quasars and far-infrared selected starburst galaxies throughout cosmic time, and follow how this relates to the processes that shape galaxies and govern the formation of stars. For this we conduct high angular resolution imaging of CO, [CII], [NII] and continuum emission of redshift 2 to 7 quasars, using the IRAM PdBI, JVLA, and ALMA.  A possible focus can be the comparison of ALMA/PdBI [CII] observations of submm galaxies with similar observations for quasars to understand whether or not the different trends in [CII] measurements for high redshift quasars applies to all high redshift objects and is thus a clear evidence for cosmological time evolution of the gas properties. In the long term we plan blind spectral surveys of [CII] for the earliest star forming galaxies using ALMA and CCAT. Latter will be the most powerful submillimeter telescope, expected to start operation in 2017 (www.ccatobservatory.org). Our group is a major partner in this project and the PhD student can play an important role in defining the first survey observations with CCAT.

 

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

 

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

                                    

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Code: UB14

A systematic search for dust excess emission in nearby galaxies

 

The spectral energy distribution (SED) provides powerful means to study galaxy  properties, such as dust content and extinction, star formation activity, ISM  heating and cooling balance. The continuum emission in the submm to radio  spectral regime originates mostly from a combination of thermal dust, free-free  and synchrotron emission. There is growing evidence from observations of nearby  starburst galaxies, low-metallicity galaxies, as well as submillimetre galaxies  for an additional emission constituent on top of these components  (provisionally quoted ``excess'' emission for lack of a conclusive  interpretation), which challenges this simple picture. At face value, a very  cold dust component with colour temperatures of 4-7~K can explain this extra  emission. This cold component could contain the bulk of the dust mass, making  the mass estimate highly uncertain. Nevertheless, modelling this excess with a  very cold dust component usually leads to low gas-to-dust ratios, in  contradiction with the low metallicities measured in the gas.  Different alternative scenarios for the origin of the additional emission in  the submm-cm regime have been suggested, e.g.: (a) a variation of the dust  emissivity spectral index related to intrinsic dust properties of amorphous  grains resulting in a flattening of the spectral shape towards long  wavelengths; (b) emission from very small spinning dust grains with a peak  frequency in the submm-cm regime; (c) cosmic microwave background (CMB)  fluctuations; (d) abundance increase of the hot, very small, stochastically  heated grains with a low dust emissivity; and (e) magnetic dipole radiation  from thermal fluctuations in the magnetisation of nanoparticles containing iron.

 

Up to now the origin of the additional emission component still remains  unidentified, and our lack of knowledge to which degree it contributes to the  Rayleigh-Jeans tail of dust emission prevents a reliable determination of the  amount of dust cooler than that responsible for the FIR peak, i.e., below  15 -- 20~K. Crucial for a better understanding are observations of the spatial  distribution of the excess emission in nearby galaxies. The advent of Herschel  and especially Planck data in the far-infrared and submm regime now enables a  systematic search for galaxies showing excess emission in their global spectral  energy distributions. The aim of this project is to identify these candidate  galaxies and subsequently provide the crucial submm/mm imaging. Ideal for this  task are the bolometer arrays GISMO and NIKA at the IRAM 30m telescope (Spain),  LABOCA at APEX (Chile), as well as the bolometers at the CCAT telescope, which  is foreseen to be operational in 2017 and for which Bonn University has   guaranteed time. The obtained imaging will be combined with Spitzer and  Herschel images to derive maps of the excess emission and its three-point  spectral energy distribution. A comparison with different ISM conditions as  traced by auxiliary multi-wavelength data shall then be used to put constraints  on the possible origin of the excess emission.

 

Contact: Prof. Dr. Frank Bertoldi (bertoldi@astro.uni-bonn.de),  Dr. Marcus Albrecht (albrecht@astro.uni-bonn.de)

 

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

                                    

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Code: UB15

The role of dust in the galaxy evolution and intra-group medium of compact groups

 

A main prediction of the cold dark matter (CDM) paradigm is the hierarchical  structure formation and consequently that galaxies are more likely to be  clustered than isolated. The clustering comprises scales from small groups to  clusters and superclusters, where galaxy groups, including the subclass of  compact groups, constitute a crucial part in this hierarchy. It has been  established that poor groups host the majority of galaxies in the local  universe, which has contributed in shifting our approach of treating  galaxies as static entities towards a more dynamical view of considering them  as interacting members of their local (baryonic and dark) environment. The low  velocity dispersions, high number densities and short crossing times   characterising compact groups bring forward interactions and mergers. This  makes compact group environments the crucial laboratories to investigate the  mechanisms related to interaction-induced star formation, galaxy evolution,  morphological transitions and the impact of the intra-group medium (IGM) in the  nearby universe. Moreover, they most closely reproduce the interaction  environment of the earlier universe when galaxies assembled through  hierarchical formation.  

 

Based on the amount and distribution of HI, an evolutionary sequence for  compact groups was suggested, where in the final phase the bulk of the neutral  gas in the disks of the galaxies has been displaced. This classification of the  evolutionary state is corroborated by a bimodality in the distribution of the  specific star formation rate and of the mid-infrared (MIR) activity. These  bimodalities and a gap in the IRAC colour-colour diagramm give evidence for an  accelerated galaxy evolution in the compact group environment. Compact groups  show mid-IR colour distributions that put them in close relation to the infall  regions of galaxy clusters. Moreover, evolved groups show a higher fraction of  early-type galaxies. These observations together led to the conclusion that  compact groups constitute local examples of the plausible building blocks of  clusters at higher redshifts. 

 

Extrapolation of near-infrared and mid-infrared data of compact groups to the  far-infrared regime by fitting spectral energy distributions has been used for  a comparison of the resulting synthetic flux densities of the entire group with  the observed values of the member galaxies. As a result the existence of cold  intra-group dust was revealed, which can be a factor 2-3 higher in emission  than the cold dust in the member galaxies. Still, deep mm and submm  measurements at resolutions that allow to map the distribution and properties  of the cold dust within group members and especially the intergalactic medium  (IGM) are yet missing. As a result, very little is known on the role that dust  plays in the evolution of compact groups and the physics of the IGM. It is  unclear to which amount compact groups can replenish the IGM with reprocessed  material in the form of diffuse tails and tidal dwarf galaxies. This is also  important in view of changing the spectra of background sources. The aim of  this project is to obtain and analyse these crucial observations using the  bolometers LABOCA at APEX (Chile) and GISMO and NIKA at the IRAM 30m telescope  (Spain). 

 

Contact: Prof. Dr. Frank Bertoldi (bertoldi@astro.uni-bonn.de),  Dr. Marcus Albrecht (albrecht@astro.uni-bonn.de)

 

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

                                    

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Code: UB16

Beyond convection: mixing processes in stellar interiors

 

For many years, stellar evolutionary calculations of the lives and nucleosynthesis in low mass stars have assumed that only convection is responsible for the internal transport of material. Yet many properties of these stars cannot be explained using just convective transport. Abundances changes at the tip of the giant branch require the existence of something other than convection. The slow neutron capture process that takes place at the very end of a low mass star's life also requires something other than convection to bring it about. Many candidate mechanisms are known, such as rotation and internal gravity waves, but our understanding of how they operate is lacking. The advent of detailed hydrodynamical simulations of stellar interiors allows us to look at fluid behaviour in stars in unprecedented detail, pointing out the flaws in current stellar evolution modelling and suggesting avenues for improvement. From the observational side, asteroseismology has developed to the point where we can now probe the deep interiors of some stars, finally allowing us to directly test our theories of the processes that take place within stars.

 

In this project, the student will investigate the effect that various non-convective mixing processes have on the evolution low-mass stars. This will include looking at how these processes affect the stellar nucleosynthesis for both light and heavy elements. In addition, the student will also determine how asteroseismic signatures are affected by non-convective mixing, and whether these signatures can be reconciled with recent observations.

 

Contact: Richard Stancliffe (rjstancl@astro.uni-bonn.de)

 

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

                                    

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Code: UB17

New observables in weak gravitational lensing magnification

 

The magnification effect of weak gravitational lensing is rapidly evolving into an observational tool to study dark matter in galaxies, galaxy clusters, and the large-scale structure of the Universe. These measurements hold the prospect of constraining the nature of dark energy, test different theories of gravity, and directly measure the masses of objects at very high redshifts. Being a young field, there are several magnification observables that have been proposed in the literature but not been measured on data. With existing data from the CFHT (Canada France Hawaii Telescope) Legacy Survey and upcoming data from KiDS (Kilo Degree Survey) such measurements should be possible. The thesis work would concentrate on achieving a first detection of cosmological density-density cross-correlations which could be used in a similar way as cosmic shear to constrain the dark energy equation of state. Furthermore, a parallel theoretical effort would be undertaken to understand the potential of magnitude-magnitude cross-correlations, which could be used in a similar way. If possible such a measurement will be tried as well.

 

Bibliography:

Hildebrandt et al. (2009), A&A 507, 683

Menard et al. (2010), MNRAS 405, 1025

Heavens & Joachimi (2011), MNRAS 415, 1681

 

Contact:  Dr. Hendrik Hildebrandt  ( hendrikhildebrandt@gmail.com ), Prof. Dr. Peter Schneider (peter@astro.uni-bonn.de)

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

 

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Code: UB18

Cosmic dust

 

All weak lensing magnification measurements are affected by dust since extinction from dust in the lenses counteracts and hence weakens the magnification of background objects. Besides yielding the crucial corrections for other magnification measurements these dust estimates are of great astrophysical interest in themselves because dust is an indispensible companion of star formation. The goal of this thesis work is to measure dust in galaxies at redshifts up to z=1.4 and at distances from the centres of the galaxies of several Mpc - something that has never been done before - employing the magnitude-shift effect of magnification. Gravitational lensing is achromatic whereas the efficiency of dust extinction depends on wavelength. Thus, simultaneous measurements of the magnitude-shift in different colour-bands can be used to disentangle the two effects. A halo-model code will be developed to analyse this signal and it will be applied to measurements from the CFHT (Canada France Hawaii Telescope) Legacy Survey as well as later from KiDS (Kilo Degree Survey). As a result this will yield a direct measurement of the average dust- and dark matter-halos of high-redshift galaxies as well as an answer to the question about the existence of inter-galactic and intra-cluster dust.

 

Bibliography:

Hildebrandt et al. (2009), A&A 507, 683

Menard et al. (2010), MNRAS 405, 1025

Seljak (2000), MNRAS 318, 203

 

Contact:  Dr. Hendrik Hildebrandt  ( hendrikhildebrandt@gmail.com ), Prof. Dr. Peter Schneider (peter@astro.uni-bonn.de)

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

 

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Code: UB19

The mass-observable relations of high-z galaxy clusters

 

Weak lensing magnification is a particularly powerful tool to study high-redshift cluster lenses because it is not limited by the requirement to resolve background sources (like weak lensing shear) and does not rely on assumptions about the dynamical state of the clusters, which might be poorly fulfilled at high redshift. The SpARCS (Spitzer Adaption of the Red-Sequence Cluster Survey) data set is one of the largest optical-infrared imaging surveys that has been used to select z>1 clusters. With additional optical data from the Canada France Hawaii Telescope, Lyman-break galaxies at even higher redshifts will be selected and used to detect the magnification signal of the SpARCS clusters and estimate their masses. The first goal of the thesis work is then to combine these mass estimates with estimates of the cluster richness/X-ray luminosity/X-ray temperature. This will yield a calibration of the high-redshift mass-observable relations with unprecedented accuracy. In a next step, the same techniques will be applied to the much larger KiDS-VIKING survey which will also detect high-redshift galaxy clusters over an area of 1500 sq. deg. The statistical power of KiDS-VIKING in combination with the accurate calibration of the mass-richness relation from SpARCS will yield important cosmological constraints with the cluster mass-function, one of the major probes of dark energy.

 

Bibliography:

Wilson et al. (2009), ApJ 698, 1943

Muzzin et al. (2009), ApJ 698, 1934

Hildebrandt et al. (2011), ApJ 733, L30

 

Contact:  Dr. Hendrik Hildebrandt  ( hendrikhildebrandt@gmail.com ), Prof. Dr. Peter Schneider (peter@astro.uni-bonn.de)

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

 

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Code: UB20

Measuring the biasing of galaxies

 

Whereas the large-scale distribution of dark matter in the Universe is not directly observable, the distribution of galaxies can be determined through galaxy redshift surveys. Often, the latter is taken as a proxy for the former, since galaxies form in the density peaks of dark matter (so-called halos). However, one expects that these two distribution are different in detail. One quantifies the relative difference between these two spatial distributions by the bias b and correlation coefficient r, which in general depend both on cosmic epoch and on spatial scale. Employing weak gravitational lensing techniques together with galaxy correlation measurements, b and r can be measured directly, with a minimum of assumptions. In the framework of this thesis, a new method for determining b and r will be developed. Applying it to extensive simulation data, the performance of the new method will be tested. Finally, it will be applied to a large new data set from the Kilo Degree Survey KiDS, which is currently ongoing and which is very well suited for this kind of measurement.

 

Bibliography:

Jullo, E. (2012), ApJ 750, 37

Schneider, P. (2006), ``Weak gravitational lensing'', arXiv:astro-ph/0509252

Simon, P. et al. (2007), A&A 461, 861

 

Contact: Prof. Dr. Peter Schneider (peter@astro.uni-bonn.de), Dr. Thomas Erben (terben@astro.uni-bonn.de)

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

 

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Code: UB21

The Kilo Degree Survey and the mean mass distribution of galaxies and clusters

 

Using the method of weak gravitational lensing, which employs the effect that light bundles are slightly distorted as they propagate through a tidal gravitational field, one can measure the mean mass profile of luminous objects, such as galaxies, groups or clusters. The accuracy of such a measurement depends on the amount of available data, its imaging quality and on the ability to estimate redshifts of galaxies from multi-band photometry (so-called photometric redshifts). In this respect, the recently started Kilo Degree Survey (KiDS) provides a unique data set, owing to its wide-field coverage of 1500 square degrees, its excellent image quality and (together with the VIKING survey) having photometry in nine optical and near-infrared bands. The thesis project will be a combination of strong participation in the analysis of the optical data from KiDS, and a scientific exploitation of the data with regards to weak lensing measurements of galaxies and clusters. Depending on the preference of the PhD candidate, the emphasis can be chosen to be on photometric redshift techniques, shear measurements, or statistical analysis, in close collaboration with other team members. 

 

Bibliography:

Erben, T. et al. (2009), A&A 493, 1197

Reyes, R. (2008) MNRAS 390, 1157

Schneider, P. (2006), ``Weak gravitational lensing'', arXiv:astro-ph/0509252

 

Contact:  Dr. Thomas Erben (terben@astro.uni-bonn.de), Prof. Dr. Peter Schneider (peter@astro.uni-bonn.de)

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

 

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University of Cologne

1st Physikalisches Institut

 

Group website

Code: UK01

Physics of Low-Luminosity Radio Nuclei

 

Aim of this project is to address the global radio and molecular gas properties of a representative sample of galaxies hosting low-luminosity quasi-stellar objects. An abundant supply of gas is necessary to fuel both the active galactic nucleus and any circum-nuclear star-burst activity of quasi-stellar objects (QSOs).  The connection between ultra-luminous infrared galaxies and the host properties of QSOs is a subject to a controversial debate. Nearby low-luminosity QSOs are ideally suited to study the properties of their host galaxies because of their higher frequency of occurrence compared to high-luminosity QSOs in the same commoving volume and because of their small cosmological distance. Representative samples are selected from QSO and radio surveys. The abundance of molecular gas and the importance of star formation is being probed through infrared-  and  mm-spectroscopy. The nuclear activity is tested through radio interferometric observations that aim at distinguishing between contributions from non-thermal nuclei and super nova remnants in these low luminosity nuclei.

 

Contact: Prof. Dr. Andreas Eckart (eckart@ph1.uni-koeln.de), Prof. Dr. J. Anton Zensus (azensus@mpifr-bonn.mpg.de)

 

Site: Cologne, 1st Physics Institute, University of Cologne

 

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Code: UK02

NIR Studies of the Black Hole at the Center of our Galaxy

 

The compact source Sgr A* that can be associated with the massive black hole at the center of the Milky Way shown a strong variability from the radio to the X-ray wavelength domain. The most recent results from a near-infrared observations revealed polarized NIR flare emission of Sgr A*. This can be interpreted as emission from spots which are on relativistic orbits around Sgr A*. Emission from a possible jet or outflow from such a disk can also contribute. We also find that the variable NIR emission of Sgr A* is highly polarized and consists of a contribution of a non- or weakly polarized main flare with highly polarized sub-flares. The flare activity shows a possible quasi-periodicity of 203 min consistent with previous observations. The highly variable and polarized emission supports that the NIR emission is non-thermal and is consistent with emission from a jet or temporary disk. Alternative explanations for the high central mass concentration involving boson or fermion balls are increasingly unlikely. Observations with the VLT, VLTI and in future with the LBT will allow us to better discriminate Sgr A* from the surrounding stars, to register the light curves with a higher signal to noise, and to further develop the theoretical models.

 

Contact: Prof. Dr. Andreas Eckart (eckart@ph1.uni-koeln.de), Dr. Thomas P. Krichbaum (tkrichbaum@mpifr-bonn.mpg.de)

 

Site: Cologne, 1st Physics Institute, University of Cologne

 

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Code: UK03

VLBI Studies of the Black Hole in the Center of our Galaxy

 

The compact radio source in the center of our Galaxy, Sagittarius A* (Sgr A*), is probably the best candidate of a super-massive black hole (with approx. 3.5 - 4 million solar masses). At centimeter wavelengths, the radio image of Sgr A* is scatter broadened, not allowing a direct view into the nucleus. At short millimeter-wavelengths, however, the scatter broadening vanishes and the underlying source begins to shine through. With Very Long Baseline Interferometry (VLBI) at 3 mm wavelengths and below, it is therefore possible to study the immediate environment of a super-massive black hole. With a spatial resolution of a few ten Schwarzschild radii, one is not too far from the scale, where general relativistic effects should become visible. Direct signatures of the metric near the black hole, e.g. a shadow (with possible distortion, depending on whether the black hole is rotating or not), are expected to become observable. A first VLBI observation at 1 mm already indicated a size of < 20 Schwarzschild radii. Clearly more data are needed to confirm and improve this first estimate. The new project focuses on more extensive mm-VLBI monitoring of Sgr A* in order to search for possible signatures of the black hole and for variations in its source structure, the latter likely being related to the observed quasi-periodic brightness variations in the infrared bands. In addition to the 3mm-VLBI monitoring of Sgr A*, it is further planned to perform new VLBI experiments at shorter wavelengths (2mm, 1mm), adding new mm-telescopes, as they now become available for VLBI.

 

Contact: Prof. Dr. Andreas Eckart (eckart@ph1.uni-koeln.de), Dr. Thomas P. Krichbaum (tkrichbaum@mpifr-bonn.mpg.de)

 

Site: Cologne, 1st Physics Institute, University of Cologne and VLBI Group at the Max Planck Institute for Radio Astronomy, Bonn

 

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Code: UK04

Near-Infrared Instrumentation for Large Interferometric Observatories

 

The 1st Physics Institute of the University of Cologne is participating in two international collaborations to develop near-infrared detector systems for leading interferometric telescopes. For the Very Large Telescope Interferometer in Chile the institute is contributing two spectrometers to the GRAVITY project, a six-baseline interferometric camera for the K band. For the Large Binocular Telescope in Arizona the institute is developing the fringe and flexure tracking unit for the LINC-NIRVANA project, a direct imaging interferometric camera for JHK bands. Both local project teams consist of senior scientists, post docs, PhD students and technicians. The student can get involved in either of the the two projects by designing and testing of actual hardware components in the laboratories of the institute, by writing of control software, or by building and operating accompanying laboratory experiments which demonstrate crucial sub-functions of the final instrument. The student will actively take part and experience the work of a distributed multi-national consortium of scientists, engineers, and technicians. Complementary to the instrumentation work and in collaboration with the MPIfR (Prof. Anton Zensus), the student will participate in the observational astronomy projects of the workgroup of Prof. Andreas Eckart covering sources that are active from the radio to the infrared wavelength domain.

 

Contact: Prof. Dr. Andreas Eckart (eckart@ph1.uni-koeln.de)

 

Site: Cologne, 1st Physics Institute, University of Cologne

 

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