Autonomous Gaussian decomposition of the Galactic Ring Survey. I. Global
  statistics and properties of the 13CO emission data
  The analysis of large molecular line surveys of the Galactic plane is
essential for our understanding of the gas kinematics on Galactic scales, in
particular its link with the formation and evolution of dense structures in the
interstellar medium. An approximation of the emission peaks with Gaussian
functions allows for an efficient and straightforward extraction of useful
physical information contained in the shape and Doppler-shifted frequency of
the emission lines contained in these enormous data sets. In this work we
present an overview and first results of a Gaussian decomposition of the entire
Galactic Ring Survey (GRS) 13CO (1-0) data that consists of about 2.3 million
spectra. We performed the decomposition with the fully automated GaussPy+
algorithm and fitted about 4.6 million Gaussian components to the GRS spectra.
We discuss the statistics of the fit components and relations between the
fitted intensities, velocity centroids, and velocity dispersions. We find that
the magnitude of the velocity dispersion values increase toward the inner
Galaxy and around the Galactic midplane, which we speculate is partly due to
the influence of the Galactic bar and regions with higher non-thermal motions
located in the midplane, respectively. We also use our decomposition results to
infer global properties of the gas emission and find that the number of fit
components used per spectrum is indicative for the amount of structure along
the line of sight. We find that the emission lines from regions located on the
far side of the Galaxy show increased velocity dispersion values, likely due to
beam averaging effects. We demonstrate how this trend has the potential to aid
in characterising Galactic structure by disentangling emission that is
belonging to the nearby Aquila Rift molecular cloud from emission that is more
likely associated with the Perseus and Outer spiral arms.
