Rotation of Two Micron All Sky Survey Clumps in Molecular Clouds

TL;DR

This study investigates the rotational characteristics of 12 molecular cloud clumps using radio telescope data, revealing how angular momentum scales with size and assessing the role of rotation in cloud stability.

Contribution

It provides new measurements of specific angular momentum in molecular cloud clumps and demonstrates a power-law relation between angular momentum and size.

Findings

Specific angular momentum (J/M) ranges from 0.0022 to 0.025 pc km s$^{-1}$.

J/M increases with radius as R^{1.58±0.11}.

Rotation energy is insufficient to prevent gravitational collapse.

Abstract

We have analyzed the rotational properties of 12 clumps using $^{13}$CO (1--0) and C$^{18}$O (1--0) maps of the Five College Radio Astronomy Observatory 13.7 m radio telescope. The clumps, located within molecular clouds, have radii ($R$) in the range of 0.06 -- 0.27\,pc. The direction of clump elongation is not correlated with the direction of the velocity gradient. We measured the specific angular momentum (J/M) to be between 0.0022 and 0.025 pc\,km\,s$^{-1}$ based on $^{13}$CO images, and between 0.0025 and 0.021 pc\,km\,s$^{-1}$ based on C$^{18}$O images. The consistency of $J/M$ based on different tracers indicates the $^{13}$CO and C$^{18}$O in dense clumps trace essentially the same material despite significantly different opacities. We also found that $J/M$ increases monotonically as a function of $R$ in power--law form, $J/M~\propto~R^{1.58~\pm~0.11}$. The ratio between rotation energy and gravitational energy, $\beta$, ranges from 0.0012 to 0.018. The small values of $\beta$ imply that rotation alone is not sufficient to support the clump against gravitational collapse.