Table 1.
Averaged derived isotopic ratios in NGC 253.
| Isotopic | Molecular | Maps (a) |
Spectra (b) |
||||
|---|---|---|---|---|---|---|---|
| ratio | ratio | unweighted | σ−weighted | snr-weighted | unweighted | σ−weighted | τ−weighted |
| 12C/13C | C18O/13C18O | 18 ± 12 | 13 ± 8 | 11 ± 5 | 22 ± 7 | 21 ± 6 | 23 ± 5 |
| 16O/18O | 13CO/13C18O | 75 ± 52 | 48 ± 30 | 40 ± 20 | 140 ± 50 | 130 ± 40 | 140 ± 40 |
| 18O/17O | C18O/C17O | 6.5 ± 3.7 | 6.2 ± 1.6 | 5.7 ± 1.6 | 4.6 ± 1.1 | 4.5 ± 0.8 | 4.7 ± 0.8 |
| 13CO/C18O | 4.5 ± 1.7 | 3.8 ± 0.6 | 3.8 ± 0.5 | 6.2 ± 1.0 | 6.1 ± 0.9 | 6.1 ± 0.9 | |
Notes.
Averages and standard deviations derived from flux density ratio maps calculated within the region of interest in Fig. 3. See Sect. 3.1.2 for details. Parameters have been calculated unweighted, as well as weighted by the σ and signal to noise in each pixel (Appendix A).
Averages and standard deviations of the mean derived from the ratios of the column densities in Table 2, measured from the extracted spectra at the positions indicated in Fig. 1. Positions with upper limits are not considered. Similarly to the maps, parameters have been calculated unweighted, weighted with the standard deviation of each measurement, and weighted with the optical depth of the 13CO transition in Table 2. See Sect. 4.1 for a discussion on the differences observed between the maps and the spectra.
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