The quest for the origin of the Milky Way's most massive stars

• Applicant: Dr. Timea Csengeri
• Subject Area: Astrophysics and Astronomy
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 263087346

Recent results from ground and space-based Galactic scale surveys reveal that the large-scale structure of the interstellar medium is regulated via fast, dynamic processes, strongly supported by numerical simulations as well. Although there is substantial progress made in the past years in our understanding of the ISM and its link to star-formation, the birth of high-mass stars (M>8Msol) is still an enigma in modern astrophysics. Growing observational evidence supports that they form from collapsing super-Jeans cores with ~3000 AU scales with up to 20-40 Msol. These mass reservoirs, which are 10-100x the local thermal Jeans-mass, are associated with flows of dense gas producing shocks also suggesting short formation timescales. Observational evidence lacks, however, of the dominant physical ingredient on small-scales allowing the formation of super-Jeans cores. Furthermore, the currently known most active star-forming sites are typically found to be associated with massive filaments, so called ridges. This project therefore addresses fundamental questions, such as: How important is the role of ridges, large-scale infall and shocks at the onset of high-mass star-formation? Do the most massive stars with 30-120Msol form the same way as the so far observed 15-20 Msol regime? These questions can only be studied now based on large, Galactic-wide samples of potential sites of the next generation of OB-type stars. Playing a key role in the ATLASGAL survey in the past three years, I realized that it provides the best sample of extremely massive young clumps. The objectives of the project are: 1) study the top-heavy fragmentation of massive clumps and reveal if high-mass stars can also form in isolation as suggested by simulations and observations of OB clusters or they necessary from only in clustered environment. I address this by examining the structure of massive clumps from pc to sub-pc scales based on extensive datasets already in hand from state-of-the-art instruments, such as APEX, the IRAM~30m telescope and interferometers, like JVLA, SMA, PdBI. 2) Flows, shocks and cooling seem to be the key to form high-mass stars therefore the importance and impact of dynamic processes need to be better characterized. I plan to exploit spectral surveys to search for kinematic and chemical signatures of flows and shocks in an unprecedentedly large sample of massive clumps. To investigate the small-scale structure of flows and its link to super-Jeans cores I will ask for ALMA observations. Altogether I propose to establish an observational census of the physical and chemical characteristics of the ISM from the scale of collapsing clumps to individual collapsing cores in order to put constrains on formation scenarios. These are the first steps towards a global understanding of how high-mass stars and rich clusters form potentially leading us to understand star-burst events and the origin of super star-clusters.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1573: Physics of the Interstellar Medium
• Participating Persons: Professor Dr. Karl M. Menten; Dr. Friedrich Wyrowski