2025A&A...704A.149G

Context. It is generally accepted that high-mass stars form through a hierarchical, multi-scale fragmentation process that range from molecular clouds down to individual protostars, involving intermediate scales such as filaments. However, a comprehensive understanding of this process remains limited due to the lack of high-resolution, multi-scale observational studies that would simultaneously probe the physical conditions across the full hierarchy of star-forming structures.
Aims. We aim to understand a coherent picture of the physical processes connecting filament formation, fragmentation, and dynamical scenario of high-mass star formation in the IRAS 19074+0752 (hereafter I19074) region.
Methods. Primarily using new 1.3 mm continuum mosaicked observations, as part of the ALMA-INFANT survey, we analyzed the S-shaped filamentary cloud I19074 at a ∼6000 AU resolution. Leveraging the multi-scale information, we investigated the filament and clump fragmentation properties, such as core separations and masses.
Results. ALMA 1.3 mm dust continuum emission reveals that the S-shaped filament consists of two physically connected components: a southern (Fs) and a northern (Fn) segment. Fn is associated with an infrared (IR)-bright HII region, while Fs appears IR-dark. The total filament length is ∼2.8 pc, with Fn and Fs spanning ∼1.0 pc and ∼1.8 pc, respectively. Their masses are ∼250-910 M_⊙, while their line masses (∼250-360 M_⊙ pc^–1) exceed the critical value for turbulence support, indicating they are gravitationally bound. The S-shaped morphology likely results from the expansion of the HII region, which swept up and compressed the northern part of the pre-existing filament into an arc-like structure in Fn; meanwhile, Fs retained a more linear form due to its greater distance from the ionized gas. Accordingly, a hybrid scenario could be responsible for Fn formation, which would combine the compression of a preexisting filament by the HII region with fresh gas accumulation into the shocked-compression layer. We extracted 26 dense cores from 1.3 mm emission with masses between 1.0 and 22.9 M_⊙, with most (92%) being gravitationally bound (α_vir ≤ 2). The core separations lack periodicity; instead, four core groups define four clumps (clumps 1-4) with masses of 110-620 M_⊙. In the Fs segment, clump 1 at its southern end could be a product of edge fragmentation, while Fn exhibits hierarchical fragmentation modes: the filamentary mode responsible for clump formation within Fn and the spherical Jeans-like mode for core formation within clumps. Hierarchical fragmentation mechanisms are identified as shocked turbulence-driven within Fn and gravity-driven inside the clumps. Most cores have high mass surface densities of Σ_core ≥ 1 g cm^–2, but with no robust identification of high-mass prestellar candidates. This favors dynamical clump-fed accretion-type over core-fed accretion-type models for high-mass star formation in I19074.
Conclusions. The S-shaped filament in the I19074 region likely formed through the interaction with an expanding H II region, with the shocked-shell fragmentation mechanism in Fn and edge fragmentation in Fs serving as pathways for producing massive, star-forming clumps. Both mechanisms contribute to high-mass star formation via a dynamical clump-fed accretion process within their respective filamentary segments.