-
They used the AT&T Bell 7m telescope to
survey 60% of the spectral range between 70-150 GHz towards Sgr B2. They found 457 lines among which more than 300 are associated
with 21 molecules: SO,
OCS, SO2, HNCS, H2CS, HNCO,NH2CN, H2CCO, HC3N, NH2CHO, CH3CN, CH3SH, CH3OH,
CH2CHCN, HC5N, CH3CHO, CH3CCH, HCOOCH3, CH3CH2CN, CH3CH2OH, and CH3OCH3,
and 31 lines remain unidentified. They found
that most of the lines are subthermal (with Tex=10~30 K, far lower than the kinetic temperature Tk=80K). The high energy transitions of CH3OH, HNCO
and SO2 and the vibrationally excited HC3N and CH3CN indicates the existence
of hot spots in the source. (from Cummins
et al., 1986ApJS...60..819C)
-
They used SEST to survey Sgr B2(N, M, NW) in
218.30-263.55 GHz range. They found 1730, 660 and 110 lines respectively. The number of unidentified lines was 337, 51, and 8. They
provided line identification tables and 90 spectral plots. N position is by far richer in emission lines than M position, while the NW position is relatively poor in spectral line emission. Most of the emission is from complex carbon-bearing molecules. Dominated species at M position are simple diatromic and triatomic molecules and other inorganic molecules, and sulfer-bearing molecular line emission is strongly peaked towards M position. Towards N and M, line emission constitutes 22% and 14% of the total flux respectively. SO2 lines are the dominent source of emission at M. (from Nummelin et
al., 1998ApJS..117..427N)
- Modeling of the continuum and molecular line emission from the Sagittarius B2 molecular cloud....(to be read) (from Lis & Goldsmith, 1990ApJ...356..195L)
- They analysed 1.3mm emission lines of 42 molecular species and other isotopic species from three positions (M, N, NW) of Sgr B2. A few complex species in and only in the N source, NH2CHO,
CH3CHO, C2H3CN, C2H5CN, CH3OCHO, exhibit anomalously strong
intensities in their intrinsically weak b- and c-type lines, which indicates the importance of FIR radiative excitation (because all these species have low-lying vibrational states). Trot upto 500K was found in M and N, but =15-50K in NW. By comparing the chemical abundances to that of Orion A, they found: (from Nummelin et al., 2000ApJS..128..213N)
(1) Hot core-type molecules like CH2NH, NH2CN, CH3CN, C2H3CN, C2H5CN, H2CS are 3-8 times more abundant in Sgr B2(N) than (M).
(2) Compact ridge-type (large oxygen-containing) species like CH3OH, CH3CHO, CH3OCHO, CH3OCH3, NH2CHO show similar or slightly enhanced abundances in N as compared to M.
(3) C2H5OH abundances are similar in N, M, and also in NW.
(4)
The SO2 and SO abundances in the M core (4x10~7 and 1x10~7, respectively) are 13 and 5 times higher than in N and are very
enhanced (103 and 102 times) as compared to NW. This is similar as in prominent Orion A outflow sources.
(5) SO18O and S18O gives 16O/18O=120, much lower than solar value of 490.
(6)
The HOCO+ ion is detected in all three positions and appears to be 3 times more abundant in the NW position. HCNH+ is seen only in NW.
(7) CH3OH is the species contributs the most line flux in N (13%) with many strong lines. The rotation diagram of it needs two-component model to fit: a cold halo of Trot = 45K and Ncol = 10^16 cm-2 and a hot core of Trot = 238K and Ncol = 5x10^18 cm-2 in N; a cold halo of Trot = 40K and Ncol = 10^16 cm-2 and a hot core of Trot = 150K and Ncol = 7.9x10^18 cm-2 in M.
(8) physical structure:
- All lines at NW and SO and SO2 in all three positions can be well fit by a single homogeneous, uniformly excited source;
- Lines of following species are obviously optically thick: SO, SO2, NO, NS, H2CS, CH2NH, HC3N, CH3CN, CH3OH, and some other diatomic and triatomic species;
- N has Trot higher than M, except the case of SO2 of which M has higher Trot;
- All lines in NW have low Trot, while in M and N, mainly following species show such low Trot (15-70K): C3H2, CH3OH (two components), CH3SH, HNCO, CH3CHO and C2H5OH.
- Molecular species with lines from vibrationally or torsionally exited states are: SO2, CH3CN, C2H3CN (skeletal bending modes), CH3OH, CH3CHO (CH3 internal rotation), HC3N (skeletal bending mode and C-C stretch), and NH2CN (NH2 inversion).
(9)
chemical structure:
- The differences of chemical abundances could be partially interfered by emission from the hot cores in M and N;
- SO, SO2, NS, H2CS seem more abundant in M than in N, while HC3N and CH3CN are more abundant in N than in M;
- SO+ was detected only in M, HCNH+ was seen only in NW, HOCO+ is more abundant in NW than in N and M;
- complex organic species such as NH2CN, NH2CHO, CH3OCHO, C2H3CN and C2H5CN are more abundant in N than in M;
- Higher abundance of some species such as NH2CN in N position could be due to higher Trot, not real chemical enhancement;
- Chemical trends by comparison to Orion:
- Sgr B2(N): Hot Core type chemistry, richer in nitriles (-CN);
- Sgr B2(M): equal mixture of Hot Core and Compact Ridge type chemistry; very high abundance of SO and SO2 (100 and 1000 times of NW) indicate outflows (similar to Orion outflow sources) .
- (from Jones et al. 2008MNRAS.386..117J)
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