PAndAS in the mist: The stellar and gaseous mass within the halos of M31
  and M33
  Large scale surveys of the prominent members of the Local Group have provided
compelling evidence for the hierarchical formation of massive galaxies,
revealing a wealth of substructure that is thought to be the debris from
ancient and on-going accretion events. In this paper, we compare two extant
surveys of the M31-M33 subgroup of galaxies; the Pan-Andromeda Archaeological
Survey (PAndAS) of the stellar structure, and a combination of observations of
the HI gaseous content, detected at 21cm. Our key finding is a marked lack of
spatial correlation between these two components on all scales, with only a few
potential overlaps between stars and gas.The paucity of spatial correlation
significantly restricts the analysis of kinematic correlations, although there
does appear to the HI kinematically associated with the Giant Stellar Stream
where it passes the disk of M31. These results demonstrate that that different
processes must significantly influence the dynamical evolution of the stellar
and HI components of substructures, such as ram pressure driving gas away from
a purely gravitational path. Detailed modelling of the offset between the
stellar and gaseous substructure will provide a determination of the properties
of the gaseous halo of M31 and M33.
