A Comparative Study of Giant Molecular Clouds in M51, M33 and the Large Magellanic Cloud

TL;DR

This study compares properties of giant molecular clouds in M51, M33, and the LMC, revealing differences in size, brightness, and velocity dispersion, and discusses how interstellar pressure influences these variations.

Contribution

It provides a comparative analysis of GMCs across three galaxies and highlights the impact of observational bias and environmental factors on GMC properties.

Findings

GMCs in M51 are larger, brighter, and have higher velocity dispersions.

No size-linewidth correlation found within individual galaxies' GMCs.

Interstellar pressure influences GMC density and velocity dispersion.

Abstract

We compare the properties of giant molecular clouds (GMCs) in M51 identified by the Plateau de Bure Interferometer Whirlpool Arcsecond Survey (PAWS) with GMCs identified in wide-field, high resolution surveys of CO emission in M33 and the Large Magellanic Cloud (LMC). We find that GMCs in M51 are larger, brighter and have higher velocity dispersions relative to their size than equivalent structures in M33 and the LMC. These differences imply that there are genuine variations in the average mass surface density of the different GMC populations. To explain this, we propose that the pressure in the interstellar medium surrounding the GMCs plays a role in regulating their density and velocity dispersion. We find no evidence for a correlation between size and linewidth in any of M51, M33 or the LMC when the CO emission is decomposed into GMCs, although moderately robust correlations are apparent when regions of contiguous CO emission (with no size limitation) are used. Our work demonstrates that observational bias remains an important obstacle to the identification and study of extragalactic GMC populations using CO emission, especially in molecule-rich galactic environments.