2023ApJ...949...46H

In order to study the initial conditions of massive star formation, we have previously built a sample of 463 high-mass starless clumps (HMSCs) across the inner Galactic plane covered by multiple continuum surveys. Here, we use ¹³CO(2-1) line data from the SEDIGISM survey, which covers 78° in longitude (-60° < l < 18°, ∣b∣ < 0.°5) with 30″ resolution, to investigate the global dynamical state of these parsec-scale HMSCs (207 sources with good-quality data, mass 10²-10⁵M_⊙, size 0.1-3.6 pc). We find that most HMSCs are highly turbulent with a median Mach number ${{ \mathcal M }}_{{ \mathcal S }}\sim 8.2$, and 44%-55% of them are gravitationally bound (with virial parameter α_vir ≲ 2) if no magnetic fields are present. A median magnetic field strength of 0.33-0.37 mG would be needed to support these bound clumps against collapse, in agreement with previous observations of magnetic fields in regions of massive star formation. Luminosity-to-mass ratio, an important tracer of evolutionary stage, is strongly correlated with dust temperature. Magnetic field strength is also correlated with density. The Larson line width-size scaling does not hold in HMSCs. This study advances our understanding of the global properties of HMSCs, and our high-resolution observations with the Atacama Large Millimeter/submillimeter Array are in progress to study the resolved properties.