Table 1
Molecular line transitions analyzed in this paper.
| Molecule | Transition | Frequency (a) | Velocity resolution | Eu∕kB | Critical density (b) | rms noise (c) |
|---|---|---|---|---|---|---|
| (MHz) | (km s−1) | (K) | ncrit (cm−3) | (mJy beam−1) | ||
| 13CO (d) | 2–1 | 220 398.68 | 2.7 | 15.9 | 9.87 × 103 | 1.99 (d) |
| H2CO | 30,3–20,2 | 218 222.19 | 0.5 | 21.0 | 3.36 × 106 | 5.29 |
| 32,2–22,1 | 218 475.63 | 0.5 | 68.1 | 2.96 × 106 | 4.58 | |
| CH3OH | 4+2,2,0–3+1,2,0 | 218 440.05 | 0.5 | 45.5 | 7.81 × 107 | 4.95 |
| CH3CN | 120–110 | 220 747.26 | 0.5 | 68.9 | 4.46 × 106 | 4.06 |
| 121–111 | 220 743.01 | 0.5 | 76.0 | 4.13 × 106 | 4.06 | |
| 122–112 | 220 730.26 | 0.5 | 97.4 | 4.19 × 106 | 4.06 | |
| 123–113 | 220 709.02 | 0.5 | 133.1 | 4.27 × 106 | 4.06 | |
| 124–114 | 220 679.29 | 0.5 | 183.1 | 3.96 × 106 | 4.06 | |
| 125–115 | 220 641.08 | 0.5 | 247.3 | 3.62 × 106 | 4.06 | |
| 126–116 | 220 594.42 | 0.5 | 325.8 | 3.68 × 106 | 4.06 | |
| DCN | 30,0–20,0 | 217 238.54 | 2.7 | 20.9 | 1.82 × 107 | 1.76 |
| SO | 56–45 | 219 949.44 | 2.7 | 35.0 | 2.31 × 106 | 2.58 |
Notes. (a) The rest frequencies were extracted from the Cologne Database for Molecular Spectroscopy (CDMS). (b) The critical density was estimated from the approximation ncrit ≈ A∕Γ (Shirley 2015), for collision rates at T = 100 K. Both, the Einstein A and the Γ coefficients were taken from the Leiden Atomic and Molecular Database (LAMDA). DCN is approximated by the corresponding values for HCN in the database. (c)The rms noise of the images was estimated from line-free channels. The beam size is 0.43′′ × 0.35′′. (d) Only for 13CO we also imaged the interferometric data merged with the single-dish data. The resulting cube has an rms noise of 2.15 mJy beam−1, with a synthesized beam of 0.8′′ × 0.67′′.
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