Properties and rotation of molecular clouds in M 33
  The sample of 566 molecular clouds identified in the CO(2--1) IRAM survey
covering the disk of M~33 is explored in detail.The clouds were found using
CPROPS and were subsequently catalogued in terms of their star-forming
properties as non-star-forming (A), with embedded star formation (B), or with
exposed star formation C.We find that the size-linewidth relation among the
M~33 clouds is quite weak but, when comparing with clouds in other nearby
galaxies, the linewidth scales with average metallicity.The linewidth and
particularly the line brightness decrease with galactocentric distance.The
large number of clouds makes it possible to calculate well-sampled cloud mass
spectra and mass spectra of subsamples.As noted earlier, but considerably
better defined here, the mass spectrum steepens (i.e. higher fraction of small
clouds) with galactocentric distance.A new finding is that the mass spectrum of
A clouds is much steeper than that of the star-forming clouds.Further dividing
the sample, this difference is strong at both large and small galactocentric
distances and the A vs C difference is a stronger effect than the inner/outer
disk difference in mass spectra.Velocity gradients are identified in the clouds
using standard techniques.The gradients are weak and are dominated by prograde
rotation; the effect is stronger for the high signal-to-noise clouds.A
discussion of the uncertainties is presented.The angular momenta are low but
compatible with at least some simulations.The cloud and galactic gradients are
similar; the cloud rotation periods are much longer than cloud lifetimes and
comparable to the galactic rotation period.The rotational kinetic energy is
1-2\% of the gravitational potential energy and the cloud edge velocity is well
below the escape velocity, such that cloud-scale rotation probably has little
influence on the evolution of molecular clouds.
