BISTRO survey: Gravity-dominated and magnetically regulated star formation in M17 SW

Zhao, Mengke, Qiu, Keping, Kang, Ji-hyun, Tang, Xindi, Whitworth, Anthony ORCID: https://orcid.org/0000-0002-1178-5486, Ward-Thompson, Derek ORCID: https://orcid.org/0000-0003-1140-2761 and Priestley, Felix 2026. BISTRO survey: Gravity-dominated and magnetically regulated star formation in M17 SW. The Astrophysical Journal 1005 (1) , 91. 10.3847/1538-4357/ae6ce5

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Abstract

We present high-resolution magnetic field maps of the M17 SW molecular cloud using JCMT 850 μm dust polarization at scale of 14″. The magnetic field exhibits a distinct arc-like structure that encircles three dense clumps (C1, C2, and C3). By combining polarization data with ammonia line observations, the plane-of-sky magnetic field strength, measured using the Skalidis–Tassis method to minimize angle dispersion errors, ranges from 0.1 to 2.4 mG (mean: 0.54 mG). Energy budget analysis reveals a hierarchy dominated by gravity (eG ≈ 10−7.8 erg cm−3), which exceeds both magnetic (eB ≈ 10−8.3 erg cm−3) and turbulent (ek ≈ 10−8.7 erg cm−3) energies. Since all three energy densities lie within 1 order of magnitude, gravitational dominance acts primarily as the global driver, while the system remains in a state of near equipartition. Structurally, the northeastern boundary shows magnetic field lines perpendicular to the shock front, consistent with compression from the adjacent H II region. Within the cloud, magnetic field lines generally align with gravity to assist collapse, but turn perpendicular to gravity within curved accretion bridges. This configuration provides support against radial collapse while guiding gas flow. Kinematic evidence suggests that these channels transport material from clump C3 onto the massive clump C2. Star formation in M17 SW is globally driven by gravity but locally regulated by the magnetic field structure.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Physics and Astronomy
Additional Information:	Full author list available at DOI. License information from Publisher: LICENSE 1: URL: https://creativecommons.org/licenses/by/4.0/, Type: cc-by
Publisher:	American Astronomical Society
ISSN:	0004-637X
Date of First Compliant Deposit:	30 June 2026
Date of Acceptance:	9 May 2026
Last Modified:	30 Jun 2026 10:53
URI:	https://orca.cardiff.ac.uk/id/eprint/187825

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