Giant Molecular Clouds in the Early-Type Galaxy NGC4526
  We present a high spatial resolution ($\approx 20$ pc) of $^{12}$CO($2-1$)
observations of the lenticular galaxy NGC4526. We identify 103 resolved Giant
Molecular Clouds (GMCs) and measure their properties: size $R$, velocity
dispersion $\sigma_v$, and luminosity $L$. This is the first GMC catalog of an
early-type galaxy. We find that the GMC population in NGC4526 is
gravitationally bound, with a virial parameter $\alpha \sim 1$. The mass
distribution, $dN/dM \propto M^{-2.39 \pm 0.03}$, is steeper than that for GMCs
in the inner Milky Way, but comparable to that found in some late-type
galaxies. We find no size-linewidth correlation for the NGC4526 clouds, in
contradiction to the expectation from Larson's relation. In general, the GMCs
in NGC4526 are more luminous, denser, and have a higher velocity dispersion
than equal size GMCs in the Milky Way and other galaxies in the Local Group.
These may be due to higher interstellar radiation field than in the Milky Way
disk and weaker external pressure than in the Galactic center. In addition, a
kinematic measurement of cloud rotation shows that the rotation is driven by
the galactic shear. For the vast majority of the clouds, the rotational energy
is less than the turbulent and gravitational energy, while the four innermost
clouds are unbound and will likely be torn apart by the strong shear at the
galactic center. We combine our data with the archival data of other galaxies
to show that the surface density $\Sigma$ of GMCs is not approximately constant
as previously believed, but varies by $\sim 3$ orders of magnitude. We also
show that the size and velocity dispersion of GMC population across galaxies
are related to the surface density, as expected from the gravitational and
pressure equilibrium, i.e. $\sigma_v R^{-1/2} \propto \Sigma^{1/2}$.
