THE JAMES CLERK MAXWELL TELESCOPE NEARBY GALAXIES LEGACY SURVEY. II. WARM MOLECULAR GAS AND STAR FORMATION IN THREE FIELD SPIRAL GALAXIES
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abstract
We present the results of large-area CO J=3-2 emission mapping of three
nearby field galaxies, NGC 628, NGC 3521, and NGC 3627, completed at the James
Clerk Maxwell Telescope as part of the Nearby Galaxies Legacy Survey. These
galaxies all have moderate to strong CO J=3-2 detections over large areas of
the fields observed by the survey, showing resolved structure and dynamics in
their warm/dense molecular gas disks. All three galaxies were part of the
Spitzer Infrared Nearby Galaxies Survey sample, and as such have excellent
published multi-wavelength ancillary data. These data sets allow us to examine
the star formation properties, gas content, and dynamics of these galaxies on
sub-kiloparsec scales. We find that the global gas depletion times for
dense/warm molecular gas in these galaxies is consistent with other results for
nearby spiral galaxies, indicating this may be independent of galaxy properties
such as structures, gas compositions, and environments. Similar to the results
from the THINGS HI survey, we do not see a correlation of the star formation
efficiency with the gas surface density consistent with the Schmidt-Kennicutt
law. Finally, we find that the star formation efficiency of the dense molecular
gas traced by CO J=3-2 is potentially flat or slightly declining as a function
of molecular gas density, the CO J=3-2/J=1-0 ratio (in contrast to the
correlation found in a previous study into the starburst galaxy M83), and the
fraction of total gas in molecular form.
