Molecular Gas Properties in M83 from CO PDFs
  We have obtained 12CO(1--0) data of the nearby barred spiral galaxy M83 from
Atacama Large Millimeter/submillimeter Array and Nobeyama 45m observations. By
combining these two data sets, the total CO flux has been recovered, and a high
angular resolution (2" corresponding to ~40 pc at the distance of M83) has been
achieved. The field of view is 3' corresponding to ~3.4 kpc and covers the
galactic center, bar, and spiral arm regions. In order to investigate how these
galactic structures affect gas properties, we have created a probability
distribution function (PDF) of the CO integrated intensity (I_CO), peak
temperature, and velocity dispersion for a region with each structure. We find
that the I_CO PDF for the bar shows a bright-end tail while that for the arm
does not. Since the star formation efficiency is lower in the bar, this
difference in PDF shape is contrary to the trend in Milky Way studies where the
bright-end tail is found for star-forming molecular clouds. While the peak
temperature PDFs are similar for bar and arm regions, velocity dispersion in
bar is systematically larger than in arm. This large velocity dispersion is
likely a major cause of the bright-end tail and of suppressed star formation.
We also investigate an effect of stellar feedback to PDF profiles and find that
the different I_CO PDFs between bar and arm regions cannot be explained by the
feedback effect, at least at the current spatial scale.
