The JCMT Nearby Galaxies Legacy Survey VIII. CO data and the
  L(CO3-2)-L(FIR) correlation in the SINGS sample
  The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey (NGLS)
comprises an HI-selected sample of 155 galaxies spanning all morphological
types with distances less than 25 Mpc. We describe the scientific goals of the
survey, the sample selection, and the observing strategy. We also present an
atlas and analysis of the CO J=3-2 maps for the 47 galaxies in the NGLS which
are also part of the Spitzer Infrared Nearby Galaxies Survey. We find a wide
range of molecular gas mass fractions in the galaxies in this sample and
explore the correlation of the far-infrared luminosity, which traces star
formation, with the CO luminosity, which traces the molecular gas mass. By
comparing the NGLS data with merging galaxies at low and high redshift which
have also been observed in the CO J=3-2 line, we show that the correlation of
far-infrared and CO luminosity shows a significant trend with luminosity. This
trend is consistent with a molecular gas depletion time which is more than an
order of magnitude faster in the merger galaxies than in nearby normal
galaxies. We also find a strong correlation of the L(FIR)/L(CO3-2) ratio with
the atomic to molecular gas mass ratio. This correlation suggests that some of
the far-infrared emission originates from dust associated with atomic gas and
that its contribution is particularly important in galaxies where most of the
gas is in the atomic phase.
