Thesis projects in high-mass star formation and the interstellar medium
Max-Planck-Institute for Astronomy (MPIA), Heidelberg/Germany
Attention: Prof. Dr. Henrik Beuther

This group studies the early evolutionary phases of high-mass star formation using state of the art (sub)millimeter wavelength interferometers as well as ground- and space-based single-dish instrunments. Massive star formation is one of the most lively evolving parts of star formation research where many exiting questions remain to be tackled. One of the main underlying question in massive star formation is whether the most massive stars form via similar physical processes like their low-mass counterparts, or whether completely different processes, for example, the coalescence and merging of intermediate-mass protostars, are important as well. The availability of (Sub)Millimeter Interferometers - already existing instruments as well as future arrays (e.g., PdBI, SMA, ALMA) - now allows to resolve the innermost regions of massive star-forming regions and thus study the physical processes in detail. These processes are for example studied with the IRAM  NOEMA large program CORE, or most recently also with JWST. In addition to these small-scale structure, the group also works on larger spatial scales associated with the formation of clouds as well as the Milky Way structure as a whole. For these questions, we are part of larger survey collaborations as well, for example, ATLASGAL or THOR that are conducted with other instruments like APEX, VLA or Herschel.

Ongoing PhD thesis projects:

Dynamical accretion flows (Molly Wells, start September 2021)
The dynamical processes during cloud and star formation are still poorly constrained. Are clouds collapsing globally or are filamentary accretion processes an indispensable part of the picture? This project will characterize the kinematical and physical properties of accretion flows from cloud to core scales by means of large observing programs conducted at ALMA & NOEMA.

Characterizing physical and chemical properties of young protostars with JWST (Simon Reyes-Reyes, start September 2023)
What are the physical and chemical properties of the warm/hot dense gas close to the forming (high-mass) protostars? The advent of JWST now allows us to characterize these properties in great detail. This thesis will start from a European MIRI consortium guaranteed time program targeting a sample of protostars with the MIRI MRS IFU. This project will investigate the properties of the accretion and outflow processes. Furthermore, atomic and molecular gas lines as well as  ice features covered by MIRI will reveal the dense core properties closely associated with the protostars and their disks.

Upcoming PhD thesis projects:

Finished PhD thesis projects:

Molecular cloud formation processes in the Milky Way (Jonas Syed, star September 2019-July 2023)
How do molecular clouds form and how does the molecular gas convert to the atomic phase? How much does environment, e.g., spiral arms or interarm regions, affect these processes? These questions will be addressed based on large-scale surveys in the atomic and molecular gas of our Milky Way. The atomic phase can be studied by means of the THOR project (The HI/OH/Recombination line survey of the Milky Way) observed with the Very Large Array (VLA). The THOR HI data will be analyzed in detail and set into context with complementary surveys of other gas tracers in the Milky Way. This northern hemisphere project will be complemented by studies of southern Giant Molecular Filaments by means of the new 13CO/C18O(2-1) survey SEDIGISM conducted with APEX.

High-mass core and disk characetrization from mid-infrared (JWST) to mm wavelength (NOEMA) (Caroline Gieser, September 2018-July 2022)
Star formation proceeds from very cold gas clumps to hot molecular cores and stars, and hence the star formation process automatically covers a broad range of temperatures.  Therefore, studying star formation in general, and high-mass star formation in particular, requires multi-wavelength studies to sample the different phases and entities within the star-forming region. Therefore, this PhD project is planed to investigate different physical processes during high-mass star formation, all related to the physical and chemical properties of the dense cores and potential accretion disks. The project will start with investigations of the core and disk properties at mm wavelengths based on the IRAM NOEMA large program CORE. Then, after the launch of JWST to happen in the first half of 2016, the project is suppose to slowly shift to the warmer gas and dust properties visible at mid-infrared wavelength based on a guaranteed time project with JWST.

The formation of disks during the early evolution of high-mass stars (Aida Ahmadi, December 2015-Januar 2020)
What are the properties of the gas during high-mass star formation? Where and how do massive accretion disks form? What are the actual infall rates - and related accretion rates - of the gas? How does the gas accrete through embedded hypercompact HII regions? These are some of the questions related to a newly established large program CORE at the Plateau de Bure Interferometer (NOEMA, formerly PdBI): Fragmentation and disk formation during high-mass star formation. This program studies a sample of 18 high-mass star-forming regions in the 1mm and 870mum band in the line and continuum emission at almost unprecedented spatial resolution of 0.2-0.3''. corresponding to linear scales of down to ~150AU for the closest target regions. Within this program, the student will focus in particular on the kinematics of the gas and the formation of accretion disks. This project includes all steps from data reduction to analysis interpretation and setting into context with theoretical models. The whole project is embedded in  a large international collaboration.

Molecular and atomic gas in the Milky Way (Michael Rugel, November 2014-November 2018)
What are the relative properties of the molecular and atomic gas in the Milky Way? How do their properties vary with for example the Galactoccentric radius of the Galactic latitude? Employing the Galacticplane survey "The HI/OH/Recombination line survey of the Milky Way" (THOR) that observes our Milky Way with the Very Large Array (VLA) between longitudes of 15 and 67 degrees and latitudes <+_1 degree) in the emission of the atomichydrogen (HI), four OH and 19 radio recombination lines, as well as the continuum emission, we can study the different phases of theinterstellar medium (ISM) in great depth. This allows not just studies of individual clouds but also investigations of the general propertieswith respect to location in our home galaxy. In addition to these scientific studies, Michael will also be involved in the data reductionand analysis of this large survey. The whole project is embedded in  a large international collaboration.

Cloud formation based on HI emission from the THOR survey
(Simon Bihr, October 2012-April 2016)
Understanding the formation of molecular clouds from the more diffuse atomic medium is central to the understanding of star formation in general. We are currently conducting "The HI/OH/Recombination line survey of the Milky Way" (THOR) which observes with the Very Large Array (VLA) a large fraction of the Galactic plane (between longitudes of 15 and 67 degrees and latitudes <+_1 degree) in the emission of the atomic hydrogen (HI), four OH and 19 radio recombination lines, as well as the continuum emission. This survey will allow us to address a plethora of scientific question associated with the formation of clouds, the embedded star formation, emerging HII regions as well as the end of the stars life. The thesis project from Simon Bihr is specifically targeting the cloud formation aspect of the project employing the HI data, and correlating them with complementary surveys, e.g., CO observations of the molecular phase. Questions to be addressed are: How does the molecular gas form out of the atomic phase? Do we find kinematic transition signatures between the different phases? How does the atomic to molecular mass ratios vary with the density of the medium? In addition to these science projects, Simon will be deeply involved in the  execution of such a large project from the planing via data reduction and analysis to the final interpretation. The whole project is embedded in  a large international collaboration.

Chemical sub-structure of high-mass star-forming regions (Siyi Feng, September 2011- February 2015)
How do the chemical properties vary within high-mass star-forming regions? The birth sites of massive stars are highly complex structures consisting of several individual gas and dust cores embedded in a less dense gas clump envelope. Furthermore, substructures like outflows and disks exist, and especially the outflows trigger shocks that can change the chemical properties of parts of the regions. Most previous chemical studies rather dealt with integrated properties from single-dish surveys, however, to disentangle the small-scale structure, interferometric observations at high-spatial-resolution will be essential. Therefore, the student will analyze and interprete interferometric observations of young high-mass star-forming regions, and set the results into context of chemical models. The observational data come from existing instruments like the SMA and PdBI, but also from the forthcoming next generation array ALMA. Furthermore, the student will likely also work with radiative transfer tools to properly model the data.

Mapping the chemistry of the interstellar medium (Thomas Gerner, April 2011 - October 2014)
The thesis project will start at large spatial scales and investigate a sample of molecular cloud complexes at different evolutionary stages in a few selected molecular species. Part of the data are already gathered prior to the thesis, and the student can straightaway dive into the data reduction and analysis. On top of that, he/she will write additional proposals to enhance the large-scale sample (2-3 more sources) with APEX, the IRAM 30m telescope and Mopra, as well as to observe dedicated sub-regions in additional spectral setups. Based on the derived results, he/she will select a few specific targets and investigate the small-scale properties with interferometers. While outcomes like the ionization fraction can be used as input parameters for theoretical models, measured abundances can be directly compared with the modeling result conducted by another student in parallel. Furthermore, the resulting spatial and kinematic information will be related to the models via the radiative transfer modeling. On top of that, we will conduct broader chemical studies of massive star-forming regions at different evolutionary stages. While the results from that study will directly constrain the changing chemical properties throughout the evolution, they again can be set into context with the modeling results from the theoretical student.

Massive star formation on Galactic scales (Jochen Tackenberg, October 2009 - April 2013)
Often studies of (massive) star formation are biased by initial sample selection criteria. However, to get a general understanding of the early evolution of young massive stars, it is important to overcome any selection bias and to study all different evolutionary stages in a statistical sense. The advent of Galactic plane surveys from near-/mid-/far-infrared wavelengths to the mm regime now allows for the first time such unbiased studies of massive star-forming regions on Galactic scales. This PhD project will start with the data from the submm wavelengths Galactic plane survey ATLASGAL (conducted with the APEX telescope in Chile) and cross-correlate a relative large fraction of the sky with the complementary mid- to far-infrared surveys avalaible from the Spitzer Space Telescope surveys GLIMPSE and MIPSGAL. These data will allow to disentangle the different evolutionary stages and hence tackle many different questions, for example it will constrain the relative time-scales during the evolution of massive stars. Follow-up steps of this project will include interefrometric case-studies of individual sources as well as analyzing complementary data from the Herschel satellite.

Disks in massive star formation (Cassie Fallscheer, August 2006 - May 2010)
The last few years have accumulated large amounts of indirect evidence that at least early B and late O stars (up to probably 20Msun) form via similar disk-accretion proecesses like their low-mass counterparts. However, all these studies were rather indirect, and the time is ripe to investigate the underlying expected accretion disks in more detail. The advent of the above mentioned (sub)mm intereferometers now allows for the first time to resolve the dense gas and dust around the central massive protostars, and hence carefully tackle these questions investigating the small-scale structure of the massive star-forming regions. Furthermore, even the most massive stars (up to 100Msun) may harbor massive disks, but their physics could be very different to their low-mass counterparts changing the actual accretion processes. This thesis project is expected to observe a sample of massive disk candidates, and investigate the physical properties and the evolution of these objects. A potential evolutionary sequence as well as expetected differences between disks around objects of different masses are possible exciting perspectives of this project. The understanding of massive accretion disks is often considered as the missing link in the understanding of massive star formation.

Fragmentation of massive star-forming clusters (Javier Rodon, July 2006 - November 2009)
The Initial Mass Function (IMF), i.e., the universal mass distribution of cluster stars and field stars, is one of the fundamental observational properties of almost all observed stellar distributions. However, until today it is not clear why the IMF is universal and at what time of the stellar cluster evolution the IMF forms. Since almost all massive stars form in a clustered mode, massive star-forming regions are the ideal environment to study the early evolution of the IMF. Furthermore, the two main theories of massive star formation - disk accretion and early fragmentation of the massive gas cores versus the coalescence and merging model - predict different shapes of the protocluster mass functions at early evolutionary stages. To resolve the dense gas and dust of the deeply embedded very young massive star-forming clusters, high-spatial resolution in the (sub)mm wavelength regime is necessary, thus requiring again (sub)mm interferometric observations. The thesis candidate is expected to observe various young massive star-forming regions in different evolutionary stages. The analysis of a statistically significant sample should allow to derive protocluster mass functions of the different regions and thus constrain whether the IMF is determined at the very beginning of massive star formation or whether  different processes during the cluster formation process contribute to the shape of the IMF. To solve the formation history of such an important universal characteristic like the IMF will be an exciting overal goal of this project.

Associated PhD thesis projects:

Theorectical investigations of accretion disks and outflows/jets in high-mass star formation (Bhargav Vaidya, co-supervised with Christian Fendt)

Clustered high-mass star formation (Yuan Wang, exchange student from Nanjing University, China)

Diploma/Master thesis projects:

Complex kinematics in 10 filamentary infrared dark clouds (David-Sebastian Kalb, June 2022- July 2023)

Filamentary accretion flows in Cygnus X's DR20 (Miriam Sawczuck, May 2021- August 2022)

HI cloud formation - Studying the ISM by mean of HI self absorption (Jonas Syed, 2018-2019)

Chemical complexity of AFGL2591 (Caroline Gieser, 2017-2018)

Fragmentation, rotation and outflows in the high-mass star-forming region IRAS23033+5951 (Felix Bosco, 2015-2016)

Kinematics, temperature and turbulence of IRDCs (Simon Bihr, July 2011 - July 2012)

Bachelor thesis projects:

Filamentary accretion flows in high-mass star-forming clouds (Jan-Erik Schneider 2023)

Magnetic fields in stellar feedback bubbles probed by the Planck-353 GHz polarization observations (Henrik Ruh 2018)

Temperature and kinematics of massive star-forming clumps (Jonas Syed, 2017)

Interferometric outflow studies of the massive star formation region IRAS19410+2336 (Felix Widmann, March to July 2014)

Interferometric imaging procedures
(Tobias Schierhuber, March to July 2014)

Characterization of Infrared Dark Clouds
(Roxana Chira, March to July 2011)