Prof. Yueh-Ning Lee & Dr. Raffaele Rani

(National Taiwan Normal University)

The nature of turbulence in molecular clouds is one of the driving factors that influence star formation efficiency. 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 efficiency that characterizes clouds in the Central Molecular Zone (CMZ). Similarly, the analysis of the Orion B molecular cloud confirmed that the dominant solenoidal turbulence is compatible with its low star formation rate. By analyzing a large sample of Galactic molecular clouds, we showed that the relative fraction of turbulent solenoidal modes decreases with a shallow gradient with distance from the Galactic center.

The shear originating from the differential Galactic rotation is another process that competes with gravity and slows down star formation. Studies of model
Galactic rotation curves have also shown that shear declines with radius and is a good candidate for much cloud formation via Kelvin-Helmholz type instabilities. In this project, we analyze the velocity gradients in the ’moment maps’ of individual clouds in the 13CO/C18O (J = 3 → 2) Heterodyne Inner Milky Way Plane Survey (CHIMPS) to estimate their rotation and consequently their relationship to Galactic shear. The sample we consider extends from the Inner to the Outer Galaxy, spanning a variety of environments. We will also explore the potential relationship between solenoidal modes and Galactic shear. This project will be supervised by Dr. Raffaele Rani (NTNU).