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