High-Mass Starless Clumps: Dynamical State and Correlation Between Physical Parameters

Abstract: 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 $^{13}$ CO(2-1) line data from the SEDIGISM survey, which covers 78$^{\circ}$ in longitude ($-60^{\circ}<l<18^{\circ}$, $\vert b\vert<0.5^{\circ}$) with 30$^{\prime \prime}$ resolution, to investigate the global dynamical state of these parsec-scale HMSCs (207 sources with good quality data, mass $10^{2}\sim 10^{5}\ \rm M_{\odot}$, size $0.1\sim3.6$ pc). We find that most HMSCs are highly turbulent with a median Mach number $\mathcal{M_{S}}\sim$ 8.2, and 44\%$\sim$55\% of them are gravitationally bound (with virial parameter $\alpha_{\rm vir} \lesssim 2$) if no magnetic fields were present. A median magnetic field strength of 0.33$\sim$0.37 mG would be needed to support these bound clumps against collapse, in agreement with previous observations of magnetic fields in massive star formation regions. Luminosity-to-mass ratio, an important tracer for evolutionary stage, is strongly correlated with dust temperature. Magnetic field strength is also correlated with density. The Larson linewidth-size scaling does not hold in HMSCs. This study advances our understanding of global properties of HMSCs, and our high-resolution ALMA observations are on the way to study the resolved properties.