10-30 MICRON MAPS OF THE CENTRAL 5 PARSECS OF THE GALAXY - HEATING OFTHE CAVITY AND NEUTRAL GAS DISK

We present 10, 20, and 30 mu m maps of the central 60 '' x 90 '' (R.A. x decl.) of the Galaxy made at approximately 4 '' resolution with the NASA/Marshall Space Flight Center bolometer array. The maps span 2.5 x 3.8 pc centered near Sgr A IRS 1 and are the first to show the therm al emission from dust particles in both the ionized cavity and the neu tral-gas ring with high sensitivity and an angular resolution as good as several arcseconds. In addition to warm dust associated with previo usly identified filaments in the central 40 '', these maps show the de tailed distribution of dust along the entire Western Are of ionized ga s at the inner edge of the neutral-gas ring. A prominent tongue of hig h 30 mu m optical depth extends from the northern part of the ring int o the cavity near IRS 1, nearly bisecting the cavity; since we detect warm dust in this 30 mu m-emitting feature, which we call the Northern Intruder, it must be heated by radiation emitted in the cavity, thus confirming previous speculations based on far-infrared and O-0 observa tions that substantial neutral material protrudes into the cavity and may constitute infalling matter that fuels the central activity. We sh ow that all the major ionized filaments (the Western Are, the Bar, the Northern Arm, and the Eastern Arm) are ionization fronts at the inter faces between low- and high-density regions, as had been previously de monstrated convincingly only for the Western Are. The locations of the se ionization fronts are consistent with the dominant UV heating and i onizing sources being centrally located in the cavity. The derived dus t temperatures strongly support this picture: they decrease away from the region of IRS 1 and Sgr A, and they drop abruptly where the gas d ensity increases at the ring. We determine that the total ultraviolet luminosity emitted by the central cluster and required to heat the dus t to the inferred temperatures is 1.7 +/- 0.5 x 10(7) L., which agrees with our derived infrared luminosity. Half of this ultraviolet lumino sity is absorbed by dust in the cavity, and more than 40% of the ultra violet radiation that propagates to the edge of the cavity is absorbed by dust in the neutral-gas ring.