  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
30m telescope, we observed two young high-mass star-forming regions, ISOSS22478
and ISOSS23053, in the 1.3mm continuum and spectral line emission at a high
angular resolution (~0.8''). Results: We resolved 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~r^2.0,
corresponding to constant mean column densities. However, with different
temperature assumptions, a steeper mass-size relation up to M~r^3.0, which
would be more likely to correspond to constant mean volume densities, cannot be
ruled out. The correlation of the core masses with their nearest neighbor
separations is consistent with thermal Jeans fragmentation. We found hardly any
core separations at the spatial resolution limit, indicating that the data
resolve the large-scale fragmentation well. Although the kinematics of the two
regions appear very different at first sight - multiple velocity components
along filaments in ISOSS22478 versus a steep velocity gradient of more than
50km/s/pc in ISOSS23053 - the findings can be explained within 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, such as
the magnetization of the gas or external shocks triggering converging gas
flows, is nonetheless not as well constrained and would require future
investigation.
