Hot Molecular Gas in the Circumnuclear Disk
  We present an analysis of archival ISO observations of pure-rotational lines
of H2 in three pointings in the central 3 parsecs of the Galaxy: toward the
Southwest region and Northeast region of the Galactic center Circumnuclear
Disk, and toward the supermassive black hole Sgr A*. We detect pure rotational
lines from 0-0 S(0) to S(13), as well as a number of rovibrationally excited
transitions. From the pure rotational lines, we are able to describe the
molecular gas with three discrete temperature components: a `hot' component
between 500-600 K, a `hotter' component at 1250-1350 K, and a `hottest'
component at > 2600 K. Toward Sgr A*, likely due to a combination of poorer
baselines and weaker emission, we only detect a single hot component, at 1100
K. The observed excitation is consistent with heating via C-shocks. We also fit
a continuous temperature distribution to the the S(1) through S(7) lines by
assuming a power-law distribution of temperatures. We measure power law indices
of n = 3.22 for the Northeast region and n = 2.83 for the Southwest region,
with a smaller index indicating a higher fraction of warm gas. These indices
are lower than those measured for other galaxies or other Galactic center
clouds, which are measured to have n= 4-6. If we extrapolate this temperature
distribution down to a cutoff temperature of 50 K, then the total molecular gas
mass that we would measure for the Southwest (Northeast) region is 32 (140) %
of the total molecular gas mass inferred from the dust emission, and 26 (125) %
of the total molecular gas mass inferred from the CO emission for these
regions. Ultimately, we find that the disagreement in the amount of mass
recovered for these two regions means that this method cannot yet be verified
to yield a reliable and independent estimate of the mass in the local region of
the Circumnuclear Disk.
