Dense, Ionized, and Neutral Gas Surrounding Sagittarius A*

We present high resolution H41a hydrogen recombination line observations ofthe 1.2' (3 pc) region surrounding Sgr A* at 92 GHz using the OVRO MillimeterArray with an angular resolution of 7" x 3" and velocity resolution of 13 km/s.New observations of H31a, H35a, H41a, and H44a lines were obtained using theNRAO 12-m telescope, and their relative line strengths are interpreted in termsof various emission mechanisms. These are the most extensive and most sensitiveobservations of recombination line to date. Observations of HCO+ (1 - 0)transition at 89 GHz are also obtained simultaneously with a 40% improvedangular resolution and 4-15 times improved sensitivity over previousobservations, and the distribution and kinematics of the dense molecular gas inthe circumnuclear disk (CND) are mapped and compared with those of the ionizedgas. The line brightness ratios of the hydrogen recombination lines areconsistent with purely spontaneous emission from 7000 K gas with n_e = 20,000cm$^{-3}$ near LTE condition. A virial analysis suggests that the mostprominent molecular gas clumps in the CND have mean densities of 10^7 cm^{-3},sufficient to withstand the tidal shear in the Galactic Center region.Therefore, these clumps may survive over several dynamical times, and the CNDmay be a dynamically stable structure. We estimate a total gas mass of 3 x 10^5solar mass for the CND. \