Unraveling the Observational Signatures of Cloud–Cloud Collision and Hub-filament Systems in W31

Abstract

To understand the formation process of massive stars, we present a multiscale and multiwavelength study of the W31 complex hosting two extended H ii regions (i.e., G10.30-0.15 (hereafter, W31-N) and G10.15-0.34 (hereafter, W31-S)) powered by a cluster of O-type stars. Several Class i protostars and a total of 49 ATLASGAL 870 μm dust clumps (at d = 3.55 kpc) are found toward the H ii regions where some of the clumps are associated with the molecular outflow activity. These results confirm the existence of a single physical system hosting the early phases of star formation. The Herschel 250 μm continuum map shows the presence of a hub-filament system (HFS) toward both W31-N and W31-S. The central hubs harbor H ii regions and they are depicted with extended structures (with T d ∼ 25–32 K) in the Herschel temperature map. In the direction of W31-S, an analysis of the NANTEN2 12CO(J = 1−0) and SEDIGISM 13CO(J = 2−1) line data supports the presence of two cloud components around 8 and 16 km s−1, and their connection in velocity space. A spatial complementary distribution between the two cloud components is also investigated toward W31-S, where the signposts of star formation, including massive O-type stars, are concentrated. These findings favor the applicability of cloud–cloud collision (CCC) around ∼2 Myr ago in W31-S. Overall, our observational findings support the theoretical scenario of CCC in W31, which explains the formation of massive stars and the existence of HFSs.

Do simulated molecular clouds look like real ones?

“…While these 'bridging features' are frequently identified in other regions (e.g. Maity et al 2022 ), their identification is somewhat subjectiv e, and man y claimed detections bear very little resemblance to the Haworth et al ( 2015 ) diagnostic. The relatively uniform increase in HCN and other line intensities with column density in three out of four clouds suggests that these collisions may be less common than is often assumed.…”

An ALMA Glimpse of Dense Molecular Filaments Associated with High-mass Protostellar Systems in the Large Magellanic Cloud

“…As disturbances from gas collisions are added to developed clouds, amplified magnetic fields significantly enhance the effective Jeans mass and then promote the formation of dense hub filaments in a short time of order 0.1 Myr after the shock compression (Inoue et al 2018). It is also worth noting that some studies, which have meticulously examined the large-scale gas motions of molecular clouds, have shown that hub filaments are embedded in the regions where interaction between two clouds is ongoing (e.g., Dewangan 2022; Maity et al 2022Maity et al , 2023. The precolliding system possibly corresponds to Stage I (Kumar et al 2020), which comprises more than two systems with individual, simple filamentary clouds in the hub-filament cluster formation evolutionary sequence.…”

Do simulated molecular clouds look like real ones?

“…While these 'bridging features' are frequently identified in other regions (e.g. Maity et al 2022), their identification is somewhat subjective, and many claimed detections bear very little resemblance to the Haworth et al (2015) diagnostic. The relatively uniform increase in HCN and other line intensities with column density in three out of four clouds suggests that these collisions may be less common than is often assumed.…”