The Arecibo Galaxy Environment Survey X: The Structure of Halo Gas
  Around M33
  As part of the HI Arecibo Galaxy Environments Survey (AGES) we have observed
5$\times$4 degrees of sky centred on M33, reaching a limiting column density of
$\sim 1.5 \times 10^{17}$ cm$^{-2}$ (line width of 10 km s$^{-1}$ and
resolution 3.5\arcmin). We particularly investigate the absence of optically
detected dwarf galaxies around M33, something that is contrary to galaxy
formation models. We identify 22 discrete HI clouds, 11 of which are new
detections. The number of objects detected and their internal velocity
dispersion distribution is consistent with expectations from standard galaxy
formation models. However, the issue remains open as to whether the observed
velocity dispersions can be used as a measure of the HI clouds total mass i.e.
are the velocities indicative of virialised structures or have they been
influenced by tidal interactions with other structures in the Local Group? We
identify one particularly interesting HI cloud, AGESM33-31, that has many of
the characteristics of HI distributed in the disc of a galaxy, yet there is no
known optical counterpart associated with it. This object has a total HI mass
of $1.22 \times 10^{7}$ M$_{\odot}$ and a diameter of 18 kpc if at the distance
of M33 ($D_{M33}=840$ kpc). However, we also find that there are numerous other
HI clouds in this region of sky that have very similar velocities and so it is
plausible that all these clouds are actually associated with debris from the
Magellanic stream.
