An inverted infall profile for the collapse of the massive star-forming IRDC SDC335.579-0.292

Xie, Jinjin, Fuller, Gary A., Li, Di, Smith, Rowan, Peretto, Nicolas ORCID: https://orcid.org/0000-0002-6893-602X, Wu, Jingwen, Wang, Yongxiong, Duan, Yan, Xia, Jifeng, Esimbek, Jarken and Baan, Willem A. 2026. An inverted infall profile for the collapse of the massive star-forming IRDC SDC335.579-0.292. Monthly Notices of the Royal Astronomical Society 548 (2) , stag644. 10.1093/mnras/stag644

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Abstract

There is increasing evidence for global collapse of clumps over parsec-scales in massive star formation regions. Such collapse may result in characteristic molecular line emission profiles but the spatial variation of such lines has rarely been quantitatively examined. Here we explore the infall properties using the spatially resolved HCO J = 1–0 and HCO J = 1–0 maps of the massive infrared dark cloud (IRDC) SDC335.579-0.292. We compare the observations with the analytical Hill5 model and radiative transfer models. This shows that the best-fitting infall velocity towards the cloud centre to be well-constrained to to km s and the mass infall rate between a few and M yr. The comparison also highlights some limitations of the Hill5 method. We demonstrate that the width of optically thin spectral lines, which are usually interpreted as resulting from turbulent motions, are in fact dominated by unresolved, ordered infall motions within the beam. Our results suggest a complex collapse situation where there is a minimum in the infall velocity at cm (0.7 pc) with the infall velocity increasing at both smaller and larger radii. The parsec-scale infall with an inverted velocity profile indicates that the accretion in this massive star-forming cloud should have intermediate scales, at which fragmentation or filament formation has to occur before material flows onto the cloud centre.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Physics and Astronomy
Additional Information:	License information from Publisher: LICENSE 1: URL: https://creativecommons.org/licenses/by/4.0/, Type: cc-by
Publisher:	Oxford University Press
ISSN:	0035-8711
Date of First Compliant Deposit:	24 April 2026
Date of Acceptance:	31 March 2026
Last Modified:	06 May 2026 09:44
URI:	https://orca.cardiff.ac.uk/id/eprint/186617

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