Table 3.
Spectral line emission properties of the vibrational transitions of HCN, HNC, and HCO+.
| Transition | Freq. | Speak | ∫S δv | Sv2 = 0 | Sv2 = 0/Sv2 = 1f | Lvib(a) |  (b) |
|---|---|---|---|---|---|---|---|
| v2 = 1f | (GHz) | (mJy) | (Jy km s−1) | (Jy) | (L⊙) | (×10−9) | |
| HCN 4 − 3 | 356.255 | 50 ± 10 | 8.0 | 6.70 ± 0.08 | 130 ± 30 | 36.3 | 1.7 |
| HCN 3 − 2 | 267.199 | 53 ± 11 | 8.5 | 6.08 ± 0.07 | 120 ± 20 | 28.9 | 1.4 |
| HCN 2 − 1 | 178.136 | 24 ± 10 | 3.8 | 3.64 ± 0.07 | 150 ± 60 | 8.5 | 0.4 |
| HNC 4 − 3 | 365.147 | 68 ± 10 | 10.8 | 3.66 ± 0.04 | 53 ± 8 | 50.2 | 2.3 |
| HNC 3 − 2 | 273.869 | 40 ± 5 | 6.4 | 3.64 ± 0.05 | 90 ± 10 | 22.3 | 1.0 |
| HCO+ 4 − 3 | 358.242 | < 38 | < 6.0 | 7.9 ± 0.1 | > 200 | < 27 | < 1.3 |
| HCO+ 3 − 2 | 268.689 | < 6.3 | < 0.95 | 6.77 ± 0.08 | > 1100 | < 3.2 | < 0.15 |
| HCO+ 2 − 1 | 179.129 | < 3.5 | < 1.6 | 3.58 ± 0.09 | > 1000 | < 3.6 | < 0.17 |
Notes. Results from Gaussian fitting individual transitions, not from the LTE model in Fig. 11, taking into account contamination from other species. Both the line fit and the upper limit calculations considers a line width of 150 km s−1, similar to that fitted to most rotational transitions.
Luminosity estimates of the vibrational emission follow Eq. (3) in Solomon & Vanden Bout (2005).
Considering an infrared luminosity of NGC 253 is LIR = 2.1 × 1010 L⊙ from Strickland et al. (2004).
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