CO(2-1) Survey at 9 parsec resolution in the SMC

TL;DR

This study presents a high-resolution CO(2-1) survey of the Small Magellanic Cloud, characterizing molecular cloud properties, dynamics, and mass distribution, revealing differences from Milky Way clouds and estimating key conversion factors.

Contribution

First detailed CO(2-1) survey of the SMC at 9 pc resolution, providing insights into molecular cloud properties and dynamics in a low-metallicity galaxy.

Findings

SMC clouds are less turbulent and less luminous than Milky Way clouds of similar size.

Derived CO-to-H2 conversion factor of 10.5 M$_{\odot}$ (K km s$^{-1}$ pc$^{2}$)$^{-1}$.

Most molecular mass in the SMC is in low-mass clouds.

Abstract

The Small Magellanic Cloud (SMC) is the closest low-metallicity galaxy to the Milky Way where the dynamical state of molecular clouds can be analyzed. We present a CO(2-1) survey at 9 pc resolution obtained with the APEX telescope in an extensive region of the SMC and characterize the properties of the molecular clouds. We study the dynamical state and stability of these clouds uniformly. We identify 177 molecular clouds within the SMC by using CPROPS, of which 124 clouds are fully resolved with signal-to-noise ratio $>$ 5. The scaling relationships show that the SMC clouds are (on average) less turbulent and less luminous than their inner Milky Way counterparts of similar size by a factor of 2 and 3, respectively, while for a fixed linewidth, the SMC clouds are over-luminous by a factor of 3.5. Using the virial masses, we derive a CO-to-H2 conversion factor for the SMC CO clouds of 10.5 M$_{\odot}(K km s^{-1} pc^{2})^{-1}$, measured at 9 pc resolution. We also determine a dust-based conversion factor of 28 M$_{\odot}(K km s^{-1} pc^{2})^{-1}$, obtained at 12 pc resolution. We find that the SMC clouds appear to be in approximate gravitational virial equilibrium. We find that the cumulative mass functions based on both the luminous mass and the virial mass are steeper than $\frac{dN}{dM} \propto M^{-2}$, suggesting that most of the molecular mass of the SMC is contained in low-mass clouds.