Rotation of Two Micron All Sky Survey Clumps in Molecular Clouds

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, ${\hat{I}}^2$, ranges from 0.0012 to 0.018. The small values of ${\hat{I}}^2$ imply that rotation alone is not sufficient to support the clump against gravitational collapse.

Accepted by Astrophysical Journal