A MULTILEVEL STUDY OF AMMONIA IN STAR-FORMING REGIONS .6. THE ENVELOPE OF SAGITTARIUS-B2

Measurements of seven metastable NH3 inversion transitions with (J,K) = (8,8), (9,9), (10,10), (11,11), (12,12), (13,13) and (14,14) are pre sented. These lines arise from energy levels between approximately 600 K and approximately 2000 K above the ground state, and are found in a bsorption toward the HII regions SgrB2(M) and (N) at epsilon(LSR)'s be tween approximately 60 and approximately 82 km s-1. Toward SgrB2(N), t here is absorption at epsilon(LSR) approximately 0 km s-1 also. The me tastable (J = K) inversion lines are collisionally excited, and an ana lysis indicates that kinetic temperatures are >600 K. The doublet leve ls are very subthermally excited, with excitation temperatures < 10 K. Thus, these lines must arise from the low density, n(H2)<5 10(3) cm-3 , extended envelope of SgrB2. In addition, we have measured absorption spectra for the epsilon = 0, J = 1 - 0 transition of SiO and the J = 4 - 3 transition of HC3N toward both sources. The absorptions are seen at epsilon(LSR)'s of approximately 0, and between 60 and 85 km s-1, a lthough the HC3N absorption SgrB2(N) is weak and blended with emission . LVG analyses of SiO and the HC3N data are consistent with H2 densiti es < 5000 cm-3. Both the NH3 and SiO results are consistent with heati ng by C shocks. These data strongly indicate that the epsilon(LSR) app roximately 0 km s-1 component is located close to the galactic center.