Fragmentation and kinematics in high-mass star formation: The CORE-extension targeting two very young high-mass star-forming regions

Context. The formation of high-mass star-forming regions from their parental gas cloud and the subsequent fragmentation processes lie at the heart of star formation research. Aims. We aim to study the dynamical and fragmentation properties at very early evolutionary stages of high-mass star formation. Methods. Employing the NOrthern Extended Millimeter Array (NOEMA) and the IRAM 30 m telescope, we observe two young high-mass starforming regions, ISOSS22478 and ISOSS23053, in the 1.3 mm continuum and spectral line emission at high angular resolution (∼0.8′′). Results. We resolve 29 cores that are mostly located along filament-like structures. Depending on the temperature assumption, these cores follow a mass-size relation of approximately M ∝ r2.0±0.3, corresponding to constant mean column densities. However, with different temperature assumptions a steeper mass-size relation up to M ∝ r3.0±0.2, that would correspond more to constant mean volume densities, cannot be ruled out. Thecorrelation of the core masses with their nearest neighbor separations is consistent with thermal Jeans fragmentation. Barely any core separationsat the spatial resolution limit are found. This indicates that the data are resolving the large-scale fragmentation well. Although the kinematics ofthe two regions appear very different at first sight – multiple velocity components along filaments in ISOSS22478 versus a steep velocity gradientof more than 50 km s−1 pc−1in ISOSS23053 – the findings can all be explained in the framework of a dynamical cloud collapse scenario. Conclusions. While our data are consistent with a dynamical cloud collapse scenario and subsequent thermal Jeans fragmentation, the importance of additional environmental properties – e.g., the magnetization of the gas or external shocks triggering converging gas flows – is still less well constrained and requires future investigation.