Detection of Widespread Hot Ammonia in the Galactic Center
  We present the detection of metastable inversion lines of ammonia from energy
levels high above the ground state. We detect these lines in both emission and
absorption toward fifteen of seventeen positions in the central 300 parsecs of
the Galaxy. In total, we observe seven metastable transitions of ammonia:
(8,8), (9,9), (10,10), (11,11), (12,12), (13,13) and (15,15), with energies (in
Kelvins) ranging from 680 to 2200 K. We also map emission from ammonia (8,8)
and (9,9) in two clouds in the Sgr A complex (M-0.02-0.07 and M-0.13-0.08), and
we find that the line emission is concentrated toward the the dense centers of
these molecular clouds. The rotational temperatures derived from the metastable
lines toward M-0.02-0.07 and M-0.13-0.08 and an additional cloud (M0.25+0.01)
range from 350 to 450 K. Similarly highly-excited lines of ammonia have
previously been observed toward Sgr B2, where gas with kinetic temperatures of
~600 K has been inferred. Our observations show that the existence of a hot
molecular gas component is not unique to Sgr B2, but rather appears common to
many Galactic center molecular clouds. In M-0.02-0.07, we find that the hot
ammonia, contributes ~10% of the cloud's total ammonia column density, and
further, that the hot ammonia in this cloud arises in gas which is extended or
uniformly distributed on ~10 arcsecond scales. We discuss the implications of
these constraints upon the nature of this hot gas component. In addition to the
detection of hot metastable ammonia line emission, we also detect for the first
time emission from nonmetastable inversion transitions of ammonia in both
M-0.02-0.07 and M-0.13-0.08.
