The JCMT Nearby Galaxies Legacy Survey X. Environmental Effects on the
  Molecular Gas and Star Formation Properties of Spiral Galaxies
  We present a study of the molecular gas properties in a sample of 98 HI -
flux selected spiral galaxies within $\sim25$ Mpc, using the CO $J=3-2$ line
observed with the James Clerk Maxwell Telescope. We use the technique of
survival analysis to incorporate galaxies with CO upper limits into our
results. Comparing the group and Virgo samples, we find a larger mean H$_{2}$
mass in the Virgo galaxies, despite their lower mean HI mass. This leads to a
significantly higher H$_{2}$ to HI ratio for Virgo galaxies. Combining our data
with complementary H$\alpha$ star formation rate measurements, Virgo galaxies
have longer molecular gas depletion times compared to group galaxies, due to
their higher H$_{2}$ masses and lower star formation rates. We suggest that the
longer depletion times may be a result of heating processes in the cluster
environment or differences in the turbulent pressure. From the full sample, we
find that the molecular gas depletion time has a positive correlation with the
stellar mass, indicative of differences in the star formation process between
low and high mass galaxies, and a negative correlation between the molecular
gas depletion time and the specific star formation rate.
