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Very Long Baseline Interferometry Group
Director: Prof. Dr. J. Anton Zensus
Group
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Code:
AZ01
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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 ŅzooÓ 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, ŅblazarsÓ 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
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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
NASAÕs 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 CreteÕs 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
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Code:
KM01
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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
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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
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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
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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
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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
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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
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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
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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
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Code:
MK01
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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
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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
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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
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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
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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
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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
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Code:
UB01
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Code:
UK01
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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
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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 20±3 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
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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
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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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