High-Resolution Images of Diffuse Neutral Clouds in the Milky Way. I.
  Observations, Imaging, and Basic Cloud Properties
  A set of diffuse interstellar clouds in the inner Galaxy within a few hundred
pc of the Galactic plane has been observed at an angular resolution of ~1
arcmin combining data from the NRAO Green Bank Telescope and the Very Large
Array. At the distance of the clouds the linear resolution ranges from ~1.9 pc
to ~2.8 pc. These clouds have been selected to be somewhat out of the Galactic
plane and are thus not confused with unrelated emission, but in other respects
they are a Galactic population. They are located near the tangent points in the
inner Galaxy, and thus at a quantifiable distance: $2.3 \leq R \leq 6.0$ kpc
from the Galactic Center, and $-1000 \leq z \leq +610$ pc from the Galactic
plane. These are the first images of the diffuse neutral HI clouds that may
constitute a considerable fraction of the ISM. Peak HI column densities range
from $N_{HI} = 0.8-2.9 \times 10^{20}$ cm$^{-2}$. Cloud diameters vary between
about 10 and 100 pc, and their HI mass spans the range from less than a hundred
to a few thousands Msun. The clouds show no morphological consistency of any
kind except that their shapes are highly irregular. One cloud may lie within
the hot wind from the nucleus of the Galaxy, and some clouds show evidence of
two distinct thermal phases as would be expected from equilibrium models of the
interstellar medium.
