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Solenoidal turbulent modes and star formation efficiency in Galactic plane molecular clouds

Rani, Raffaele, Moore, Toby J T, Eden, David J and Rigby, Andrew J 2022. Solenoidal turbulent modes and star formation efficiency in Galactic plane molecular clouds. Monthly Notices of the Royal Astronomical Society 515 (1) , pp. 271-285. 10.1093/mnras/stac1812

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It is speculated that the high star formation efficiency observed in spiral-arm molecular clouds is linked to the prevalence of compressive (curl-free) turbulent modes, while the shear-driven solenoidal (divergence-free) modes appear to be the main cause of the low star formation efficiency that characterizes clouds in the Central Molecular Zone. Similarly, analysis of the Orion B molecular cloud has confirmed that, although turbulent modes vary locally and at different scales within the cloud, the dominant solenoidal turbulence is compatible with its low star formation rate. This evidence points to intercloud and intracloud fluctuations of the solenoidal modes being an agent for the variability of star formation efficiency. We present a quantitative estimation of the relative fractions of momentum density in the solenoidal modes of turbulence in a large sample of plane molecular clouds in the 13CO/C18O (J = 3 → 2) Heterodyne Inner Milky Way Plane Survey (CHIMPS). We find a negative correlation between the solenoidal fraction and star formation efficiency. This feature is consistent with the hypothesis that solenoidal modes prevent or slow down the collapse of dense cores. In addition, the relative power in the solenoidal modes of turbulence (solenoidal fraction) appears to be higher in the Inner Galaxy declining with a shallow gradient with increasing Galactocentric distance. Outside the Inner Galaxy, the slowly, monotonically declining values suggest that the solenoidal fraction is unaffected by the spiral arms.

Item Type: Article
Date Type: Published Online
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 0035-8711
Date of First Compliant Deposit: 27 January 2023
Date of Acceptance: 27 June 2022
Last Modified: 03 May 2023 07:45

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