Star formation scales and efficiency in Galactic spiral arms
  We positionally match a sample of infrared-selected young stellar objects
(YSOs), identified by combining the Spitzer GLIMPSE, WISE and Herschel Space
Observatory Hi-GAL surveys, to the dense clumps identified in the millimetre
continuum by the Bolocam Galactic Plane Survey in two Galactic lines of sight
centred towards l = 30deg and l = 40deg. We calculate the ratio of infrared
luminosity, L_IR, to the mass of the clump, M_clump, in a variety of Galactic
environments and find it to be somewhat enhanced in spiral arms compared to the
interarm regions when averaged over kiloparsec scales. We find no compelling
evidence that these changes are due to the mechanical influence of the spiral
arm on the star-formation efficiency rather than, e.g., different gradients in
the star-formation rate due to patchy or intermittent star formation, or local
variations that are not averaged out due to small source samples. The largest
variation in L_IR/M_clump is found in individual clump values, which follow a
log-normal distribution and have a range of over three orders of magnitude.
This spread is intrinsic as no dependence of L_IR/M_clump with M_clump was
found. No difference was found in the luminosity distribution of sources in the
arm and interarm samples and a strong linear correlation was found between L_IR
and M_clump.
