FIR Spectroscopy of the Galactic Center: Hot and Warm Molecular Gas
  The angular resolution (~10") achieved by the Herschel Space Observatory
~3.5m telescope at FIR wavelengths allowed us to roughly separate the emission
toward the inner parsec of the galaxy (the central cavity) from that of the
surrounding circumnuclear disk (the CND). The FIR spectrum toward SgrA* is
dominated by intense [Oiii], [Oi], [Cii], [Niii], [Nii], and [Ci]
fine-structure lines (in decreasing order of luminosity) arising in gas
irradiated by the strong UV field from the central stellar cluster. The high-J
CO rotational line intensities observed at the interface between the inner CND
and the central cavity are consistent with a hot isothermal component at
T~10^{3.1} K and n(H_2)~10^4 cm^{-3}. They are also consistent with a
distribution of lower temperatures at higher gas density, with most CO at T~300
K. The hot CO component (either the bulk of the CO column density or just a
small fraction depending on the above scenario) likely results from a
combination of UV and shock-driven heating. Although this component is beam
diluted in our FIR observations, it may be resolved at much higher angular
resolution. An ALMA project using different molecular tracers to characterize
UV-irradiated shocks in the innermost layers of the CND is ongoing.
