A multilevel study of ammonia in star-forming regions. VI. The envelope of Sagittarius B2.
Abstract
Measurements of seven metastable NH_3_ inversion transitions with (J,K)=(8,8), (9,9), (10,10), (11,11), (12,12), (13,13) and (14,14) are presented. These lines arise from energy levels between ~600K and ~2000K above the ground state, and are found in absorption toward the HII regions SgrB2(M) and (N) at v_LSR_'s between ~60 and ~82km/s. Toward SgrB2(N), there is absorption at v_LSR_~0km/s also. The metastable (J=K) inversion lines are collisionally excited, and an analysis indicates that kinetic temperatures are >600K. The doublet levels are very subthermally excited, with excitation temperatures <10K. Thus, these lines must arise from the low density, n(H_2_)<5 10^3^cm^-3^, extended envelope of SgrB2. In addition, we have measured absorption spectra for the v=0, J=1-0 transition of SiO and the J=4-3 transition of HC_3_N toward both sources. The absorptions are seen at v_LSR_'s of ~0, and between 60 and 85km/s, although the HC_3_N absorption SgrB2(N) is weak and blended with emission. LVG analyses of SiO and the HC_3_N data are consistent with H_2_ densities <5000cm^-3^. Both the NH_3_ and SiO results are consistent with heating by C shocks. These data strongly indicate that the v_LSR_~0km/s component is located close to the galactic center.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- February 1995
- Bibcode:
- 1995A&A...294..667H
- Keywords:
-
- Absorption Spectra;
- Ammonia;
- Energy Levels;
- H Ii Regions;
- Molecular Clouds;
- Star Formation;
- Electron Transitions;
- Interstellar Matter;
- Inversions;
- Astrophysics;
- GALAXY: CENTER;
- ISM: ABUNDANCES;
- ISM: INDIVIDUAL OBJECTS: SGRB2;
- ISM: MOLECULES;
- RADIO LINES: ISM