The nature of turbulence in molecular clouds is one of the driving factors that
influence star formation. It is speculated that the high star formation efficiency
observed in spiral-arm 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 rate that characterises
clouds in the Central Molecular Zone (CMZ). Similarly, the analysis of the
Orion B molecular cloud 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 inter-and
intra-cloud fluctuations of the solenoidal modes being an agent for the variability
of star formation efficiency.
We present a quantitative estimation of the fraction of momentum density
(ρv) power contained in the solenoidal modes of the turbulence in a large sam-
ple of plane molecular clouds in the 13CO/C18O (J = 3 → 2) Heterodyne Inner
Milky Way Plane Survey (CHIMPS). Our goal is to investigate how the fraction
of solenoidal modes may probe the variation of the star formation efficiency
in different Galactic molecular environments by comparing the “solenoidal fraction” across clouds with varying features to the clouds’ star-formation efficiency,
derived independently.