SEDIGISM-ATLASGAL: Dense Gas Fraction and Star Formation Efficiency
  Across the Galactic Disk
  By combining two surveys covering a large fraction of the molecular material
in the Galactic disk we investigate the role the spiral arms play in the star
formation process. We have matched clumps identified by ATLASGAL with their
parental GMCs as identified by SEDIGISM, and use these giant molecular cloud
(GMC) masses, the bolometric luminosities, and integrated clump masses obtained
in a concurrent paper to estimate the dense gas fractions (DGF$_{\rm gmc}=\sum
M_{\rm clump}/M_{\rm gmc}$) and the instantaneous star forming efficiencies
(i.e., SFE$_{\rm gmc} = \sum L_{\rm clump}/M_{\rm gmc}$). We find that the
molecular material associated with ATLASGAL clumps is concentrated in the
spiral arms ($\sim$60% found within $\pm$10 km s$^{-1}$ of an arm). We have
searched for variations in the values of these physical parameters with respect
to their proximity to the spiral arms, but find no evidence for any enhancement
that might be attributable to the spiral arms. The combined results from a
number of similar studies based on different surveys indicate that, while
spiral-arm location plays a role in cloud formation and HI to H$_2$ conversion,
the subsequent star formation processes appear to depend more on local
environment effects. This leads us to conclude that the enhanced star formation
activity seen towards the spiral arms is the result of source crowding rather
than the consequence of a any physical process.
