Table 7.
Comparison of the hydrogen number densities of the gas in the northeast (zone 1) of VLA 2.
| (1) | (2) | (3) | (4) | (5) |
|---|---|---|---|---|
| Epoch | Maser | |B| | nH2 | nH2(a) |
| feature | (G) | equation | (cm−3) | |
| 2005.89 (b) | VLA 2.16, VLA 2.17 | 3.4 (c) | n1 | 1.2 × 109 |
| VLA 2.22, VLA 2.24 | ||||
| 2012.54 (d) | VLA2.44 | 1.5 | n2 = 0.3 × n1 | 3.6 × 108 |
| 2016.45 | VLA2.2.27 | 27.8 | n3 = 89 × n2 | 3.2 × 1010 |
| 2018.44 | VLA2.3.39 | 0.6 | n4 = 0.003 × n3 | 108 |
| 2020.82 | VLA2.4.27 | 0.6 | n5 = n4 | 108 |
Notes.
The hydrogen number densities nH2 is calculated by considering the empirical equation 
by Crutcher et al. (2010). We assume that n5 is the lowest possible hydrogen number density for producing 22 GHz H2O maser emission, i.e. 108 cm−3 (Elitzur et al. 1989).
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