Spitzer Infrared Spectrograph Observations of the Galactic Center:
  Quantifying the Extreme Ultraviolet/so ft X-ray fluxes
  It has long been shown that the extreme ultraviolet spectrum of the ionizing
stars of H II regions can be estimated by comparing the observed line emission
to detailed models. In the Galactic Center (GC), however, previous observations
have shown that the ionizing spectral energy distribution (SED) of the local
photon field is strange, producing both very low excitation ionized gas
(indicative of ionization by late O stars) and also widespread diffuse emission
from atoms too highly ionized to be found in normal H II regions. This paper
describes the analysis of all the GC spectra taken by Spitzer's Infrared
Spectrograph and downloaded from the Spitzer Heritage Archive. In it, H II
region densities and abundances are described, and serendipitously discovered
candidate planetary nebulae, compact shocks, and candidate young stellar
objects are tabulated. Models were computed with Cloudy, using SEDs from
Starburst99 plus additional X-rays, and compared to the observed mid-infrared
forbidden and recombination lines. The ages inferred from the model fits do not
agree with recent proposed star formation sequences (star formation in the GC
occurring along streams of gas with density enhancements caused by close
encounters with the black hole, Sgr A*), with Sgr~B1, Sgr~C, and the Arches
Cluster being all about the same age, around 4.5 Myr old, with similar X-ray
requirements. The fits for the Quintuplet Cluster appear to give a younger age,
but that could be caused by higher-energy photons from shocks from stellar
winds or from a supernova.
