Cloud Properties and Star Formation in M31

TL;DR

This study catalogs 453 molecular clouds in M31, analyzing their physical properties, relationships, and star formation activity, revealing similarities and differences with Milky Way clouds and insights into star formation laws at small scales.

Contribution

First detailed catalog of molecular clouds in M31 using dendrogram analysis, including size, mass, velocity dispersion, and star formation correlations.

Findings

Most clouds are gravitationally bound.

Size-velocity dispersion relationship matches Milky Way.

Size-mass relationship is shallower than in MW clouds.

Abstract

We present a catalogue of 453 molecular clouds in M31 extracted from CO J=1-0 data observed with CARMA using a dendrogram. Our clouds have the mean values of 2.8 km s$^{-1}$, 22.1 pc and 10$^{5.2}$ M$_\odot$ for the velocity dispersion, radius and mass, respectively. The velocity dispersion shows a weak anti-correlation with the galactocentric radius. The clouds in M31 show mean and median values of 2.0 and 1.4, respectively, for their virial parameters, indicating that most of them are gravitationally bound. Our dendrogram analysis identifies 35 sources with multiple velocity components, which we classify as molecular cloud complexes. We study the size-velocity dispersion and size-mass relationships for the clouds in M31, finding the slopes of 0.43$\pm$0.05 and 1.36$\pm$0.06 for the former and the latter, respectively. Our size-velocity dispersion relationship agrees with those of Milky Way (MW) and M31 clouds. The slope of our size-mass relationship is shallower than those in clouds and cloud complexes of the MW. We find offsets between the isosurfaces of the clouds and star formation rate (SFR) peaks in M31, supporting the scenario where the evolutionary state of individual sources plays a role in the Kennicutt-Schmidt (KS) law at parsec scales. We find a slope of 0.66$\pm$0.07 for the KS law, which is slightly lower than the values of $\sim$0.8 for MW clouds.