Gas, Dust, Stars, Star Formation and their Evolution in M33 at Giant Molecular Cloud Scales

TL;DR

This study analyzes giant molecular clouds in M33, revealing their evolutionary stages, interstellar matter content, and star formation activity through principal component analysis, and finds dust correlates strongly with star formation.

Contribution

It provides a multi-parameter analysis of GMCs in M33, identifying key relations and evolutionary trends using PCA, and highlights dust as a better tracer of molecular gas than CO.

Findings

Young GMCs have lower ISM content and star formation activity.

Dust correlates more strongly with star formation rate than CO lines.

GMCs may grow denser and more massive via aggregation in early stages.

Abstract

We report on a multi parameter analysis of giant molecular clouds (GMCs) in the nearby spiral galaxy M33. A catalog of GMCs identifed in 12CO(J=3-2) was used to compile associated 12CO(J=1-0), dust, stellar mass and star formation rate. Each of the 58 GMCs are categorized by their evolutionary stage. Applying the principal component analysis on these parameters, we construct two principal components PC1 and PC2 which retain 75% of the information in the original dataset. PC1 is interpreted as expressing the total interstellar matter content, and PC2 as the total activity of star formation. Young (<10Myr) GMCs occupy a distinct region in the PC1-PC2 plane, with lower ISM content and star formation activity compared to intermediate age and older clouds. Comparison of average cloud properties in different evolutionary stages imply that GMCs may be heated or grow denser and more massive via aggregation of diffuse material in their first ~10 Myr. The PCA also objectively identified a set of tight relations between ISM and star formation. The ratio of the two CO lines is nearly constant, but weakly modulated by massive star formation. Dust is more strongly correlated with the star formation rate than the CO lines, supporting recent findings that dust may trace molecular gas better than CO. Stellar mass contributes weakly to the star formation rate, reminiscent of an extended form of the Schmidt Kennicutt relation with the molecular gas term substituted by dust.