Cataloguing Molecular Cloud Populations in Galaxy M100

Abstract

We compare the properties of giant molecular associations in the galaxy Messier 100 (M100) with those of the less massive giant molecular clouds in the Milky Way and Local Group, while also observing how those properties change within M100 itself. From this analysis of cloud mass, radius, and velocity dispersion, we determine that the clouds are in or near virial equilibrium and that their properties are consistent with the underlying trends for the Milky Way. We find differences between nuclear, arm and inter-arm M100 populations, such as the nuclear clouds being the most massive and turbulent, and arm and inter-arm populations having differently shaped mass distributions from one another. Through the analysis of velocity gradients, cloud motion can be attributed to turbulence rather than large scale shearing motion. This is supported by our comparison with turbulence regulated star formation models. Finally, we calculate ISM depletion times to see how quickly clouds turn gas into stars and found that clouds form stars more efficiently if they are turbulent or dense.

INTRODUCTION

Molecular clouds are cold, dense regions of interstellar medium where gravity is able to overcome gas pressure, enabling them to be the sole location of star formation. An improved understanding of the structure of molecular clouds will provide insight into star formation. Here, we catalogue the molecular clouds in the spiral galaxy Messier 100 (M100) of the Virgo cluster to determine whether they follow the behaviours found in previous studies (Solomon et al., 1987) (Fukui et al., 2010). At masses greater than \(10^{5}M_{\odot}\), molecular clouds fall into the range of Giant Molecular Clouds (GMCs). However, due to M100’s distance of 14.3 Mpc from earth, and the large resolution element of our observations compared to the size of typical GMCs, we are looking at complexes of GMCs called Giant Molecular Associations (GMAs). We determine whether traditional scalings extend to these larger, more massive regions. We also analyze how cloud properties differ between populations within the galaxy. We seek to understand these molecular cloud properties to gain insight into their motion, evolution, and ability to form stars.