Unearthing Foundations of a Cosmic Cathedral: Searching the Stars for
  M33's Halo
  We use data from the Pan-Andromeda Archaeological Survey (PAndAS) to search
for evidence of an extended halo component belonging to M33 (the Triangulum
Galaxy). We identify a population of red giant branch (RGB) stars at large
radii from M33's disk whose connection to the recently discovered extended
"disk substructure" is ambiguous, and which may represent a "bona-fide" halo
component. After first correcting for contamination from the Milky Way
foreground population and misidentified background galaxies, we average the
radial density of RGB candidate stars over circular annuli centered on the
galaxy and away from the disk substructure. We find evidence of a
low-luminosity, centrally concentrated component that is everywhere in our data
fainter than mu_V ~ 33 mag arcsec^(-2). The scale length of this feature is not
well constrained by our data, but it appears to be of order r_exp ~ 20 kpc;
there is weak evidence to suggest it is not azimuthally symmetric. Inspection
of the overall CMD for this region that specifically clips out the disk
substructure reveals that this residual RGB population is consistent with an
old population with a photometric metallicity of around [Fe/H] ~ -2 dex, but
some residual contamination from the disk substructure appears to remain. We
discuss the likelihood that our findings represent a bona-fide halo in M33,
rather than extended emission from the disk substructure. We interpret our
findings in terms of an upper limit to M33's halo that is a few percent of its
total luminosity, although its actual luminosity is likely much less.
