Feedback in Forming Star Clusters: The Mass-Radius Relation and Mass Function of Molecular Clumps in the Large Magellanic Cloud

Abstract

We derive the mass-radius relation and mass function of molecular clumps in the Large Magellanic Cloud (LMC) and interpret them in terms of the simple feedback model proposed by Fall, Krumholz, and Matzner (FKM). Our work utilizes the dendrogram-based catalog of clumps compiled by Wong et al. from ${}^{12}$CO and ${}^{13}$CO maps of six giant molecular clouds in the LMC observed with the Atacama Large Millimeter Array (ALMA). The Magellanic Clouds are the only external galaxies for which this type of analysis is possible at the necessary spatial resolution ($\sim 1$ pc). We find that the mass-radius relation and mass function of LMC clumps have power-law forms, $R\propto M^{\hat{I}}\pm$ and $dN/dM\propto M^2$, with indices $\hat{I}\pm =0.36\pm 0.03$ and ${\hat{I}}^2=-1.8\pm 0.1$ over the mass ranges $10^2{M}_{\odot }\lesssim M\lesssim 10^5{M}_{\odot }$ and $10^2{M}_{\odot }\lesssim M\lesssim 10^4{M}_{\odot }$, respectively. With these values of $\hat{I}\pm$ and ${\hat{I}}^2$ for the clumps (i.e., protoclusters), the predicted index for the mass function of young LMC clusters from the FKM model is ${\hat{I}}^2\approx 1.7$, in good agreement with the observed index. The situation portrayed here for clumps and clusters in the LMC replicates that in the Milky Way.

18 pages, 5 figures; accepted for publication in the Astrophysical Journal