Multi-scale view of the S-shaped high-mass star-forming filament IRAS 19074+0752 observed as part of the INFANT survey

¹ School of Physics and Astronomy, Yunnan University, Kunming 650091, PR China
² Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
³ State Key Laboratory of Radio Astronomy and Technology, A20 Datun Road, Chaoyang District, Beijing 100101, PR China
⁴ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁵ Department of Physics, National Sun Yat-Sen University, No. 70, Lien-Hai Road, Kaohsiung City 80424, Taiwan, ROC
⁶ Center for Astrophysics, Harvard & Smithsonian, MS-42, 60 Garden Street, Cambridge, MA 02138, USA
⁷ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China
⁸ Max Planck Institute for Astronomy, Konigstuhl 17, 69117 Heideberg, Germany
⁹ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia, Michoacán 58089, México
¹⁰ Department of Astronomy, The University of Tokyo, Hongo, Tokyo 113-0033, Japan
¹¹ Department of Astronomy, Xiamen University, Zengcuo’an West Road, Xiamen 361005, PR China
¹² Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, PR China
¹³ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstr. 1, 85748 Garching bei München, Germany
¹⁴ School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing 210023, PR China
¹⁵ Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210023, PR China
¹⁶ Department of Earth and Planetary Sciences, Institute of Science Tokyo, Meguro, Tokyo 152-8551, Japan
¹⁷ Joint Alma Observatory (JAO), Alonso de Córdova 3107, Vitacura, Santiago, Chile

^★ These authors contributed equally to this work.
^★★ Corresponding authors: hongliliu2012@gmail.com; xinglv.nju@gmail.com; ycheng.astro@gmail.com

Received: 24 July 2025
Accepted: 9 October 2025

Abstract

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.