Hubble Space Telescope FUV observations of M31's globular clusters
  suggest a spatially homogeneous helium-enriched sub population
  We present high spatial resolution, far ultraviolet (FUV) F140LP observations
of 12 massive globular clusters in M 31 obtained using the ACS/SBC on the
Hubble Space Telescope (HST). These observations resolve the cluster profiles
to scales similar to their core radii and enable the study of the spatial
distribution of blue and extreme horizontal branch (HB) stars, which dominate
the emission in the F140LP images. We confirm that some of these clusters have
excess FUV emission, suggesting additional hot populations beyond those
expected by canonical single stellar populations models. We find no evidence
that the hot populations are spatially distinct from the majority populations
in these clusters, as would be expected if the excess FUV emission is a result
of a dynamically enhanced population of extreme-HB stars. We conclude that a
second population of stars with significantly enhanced helium abundance is a
viable explanation for the observed FUV emission which is both bright and
distributed similarly to the rest of the cluster light. Our results support the
use of FUV observations as a path to characterising helium enhanced sub
populations in extragalactic clusters. These M31 clusters also show a
correlation such that more massive and denser clusters are relatively FUV
bright. Similar to extant Milky Way results, this may indicate the degree of
helium enrichment, or second population fraction increases with cluster mass.
