Project B1

Giant molecular clouds host the birthplaces of massive stars. Within them, coherent overdensities in form of parsec-scale massive dense clumps are the nurseries of star clusters. Fragmentation of the clumps then leads to the formation of individual stars or multiple systems. Current theoretical concepts triggered by new observational results focus more and more on the larger-scale environment of these birthplaces as crucial structures channelling the inflow of material from parsec scales to scales of disks and stars (see e. g. the global hierarchical collapse by Vázquez-Semadeni et al., MNRAS 490, 3061, 2019, and the inertial-inflow model by Padoan et al., ApJ 900, 82, 2020). Hence, the cloud and clump reservoirs are essential for the formation of massive star clusters that subsequently disperse first their clump environment and with time the larger-scale molecular cloud structures.

Here we aim at characterising in detail the important gas properties on clump scales of a fraction of a parsec to several parsecs, bridging the gap between high angular resolution studies, as conducted in Project Section A and the larger cloud scales, that can now be resolved in nearby galaxies. While the last years have seen significant progress in unbiased surveys revealing complete samples of dense clumps in our Milky Way (e.g. ATLASGAL, Urquhart et al., MNRAS 473, 1059, 2018, and HiGAL, Elia et al., MNRAS 504, 2742, 2021), the processes governing the formation and dispersion of these clumps remain poorly understood. Also from the theoretical side there is still an ongoing debate to which extent clumps and cores are gravitationally bound structures or, at least to some fraction, transient features (e.g. Ballesteros-Paredes et al., MNRAS 479, 2112, 2018). This question holds even more true for the ambient gas feeding these structures, reflected in concurring models of molecular clouds (e.g. the gravo-turbulent model, e.g. Klessen, ApJ 556, 837, 2001 vs. the global, hierachical collapse model, e. g. Vázquez-Semadeni et al., MNRAS 490, 3061, 2019). In B1 we plan to approach this topic from the observational and theoretical side by means of two different work packages (WPs), B1.1 and B1.2.