Deep neutral hydrogen observations of Leo T with the Westerbork
  Synthesis Radio Telescope
  Leo T is the lowest mass gas-rich galaxy currently known and studies of its
gas content help us understand how such marginal galaxies survive and form
stars. We present deep neutral hydrogen (HI) observations from the Westerbork
Synthesis Radio Telescope in order to understand its HI distribution and
potential for star formation. We find a larger HI line flux than the previously
accepted value, resulting in a 50% larger HI mass of 4.1 x 10^5 Msun. The
additional HI flux is from low surface brightness emission that was previously
missed; with careful masking this emission can be recovered even in shallower
data. We perform a Gaussian spectral decomposition to find a cool neutral
medium component (CNM) with a mass of 3.7 x 10^4 Msun, or almost 10% of the
total HI mass. Leo T has no HI emission extending from the main HI body, but
there is evidence of interaction with the Milky Way circumgalactic medium in
both a potential truncation of the HI body and the offset of the peak HI
distribution from the optical center. The CNM component of Leo T is large when
compared to other dwarf galaxies, even though Leo T is not currently forming
stars and has a lower star formation efficiency than other gas-rich dwarf
galaxies. However, the HI column density associated with the CNM component in
Leo T is low. One possible explanation is the large CNM component is not
related to star formation potential but rather a recent, transient phenomenon
related to the interaction of Leo T with the Milky Way circumgalactic medium.
