Abstract
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 and the IRAM 30 m telescope, we observed two young high-mass star-forming regions, ISOSS22478 and ISOSS23053, in the 1.3 mm 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 ∝ 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, 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 50 km s−1 pc−1 in ISOSS23053 – the findings can all 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.
Highlights
During the hierarchical process of star formation, the gas has to flow from the large cloud scales down to the smallest scales, where disks and protostars form
The top-left panel shows the column density against the core mass, and we find a clear correlation between the two parameters, independent of the temperature ausmsunmdpetniosinti.eWs bheiltewfeoernththeeTtHw2oCOreagpipornosacohv,ertlhaepmstarsosnegslya,nidnctohleT20 K approach, the estimated masses and column densities are larger for ISOSS23053
Fragmentation Comparing the estimated masses and column densities to the corresponding values of the original CORE study of 20 highmass star-forming regions in the more evolved evolutionary stages of high-mass protostellar objects (HMPOs), massive young stellar objects, and ultracompact HII regions (Beuther et al 2018), we find that the masses are covering a similar range
Summary
During the hierarchical process of star formation, the gas has to flow from the large cloud scales down to the smallest scales, where disks and protostars form. While questions regarding the small-scale structure and the presence of disks toward more evolved high-mass protostellar objects have been subject to intense study for several decades (e.g., Cesaroni et al 2007; Beltrán & de Wit 2016; Beuther et al 2018), the earliest evolutionary stages of collapse and fragmentation during the formation processes of high-mass stars have not been investigated in depth far. They may fragment into more massive cores with potentially less low-mass cores early on (e.g., Tan et al 2014; Zhang et al 2015; Csengeri et al 2017; Beuther et al 2018)? We ask how important filamentary accretion processes are (e.g., Schneider et al 2010; Peretto et al 2014; André et al 2014; Chira et al 2018; Hennebelle 2018; Padoan et al 2020) and what the relative importance is of cloud-scale gravo-turbulent or thermal fragmentation versus fragmentation of the gravitationally
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