A spatially resolved study of ionized regions in galaxies at different ...

164 Appendix B
Sulphur
As in the case of [Oii], the temperature of [Sii] depends on density (np 3 ions). The ratio
used to estimate t([Sii]) is
R ′ S2 =
I(6717Å) + I(6731Å)
I(4068Å) + I(4076Å)
If one of the [Sii] auroral lines cannot be measured, the theoretical ratio can be used,
I(4068Å) ≈ 3 · I(4067Å). Then, the temperature is calculated
where
t([Sii]) = a 0 (n) + a 1 (n) · R ′ S2 + a 2(n)
R ′ S2
+ a 3(n)
R ′ S2
a 0 (n) = 1.92 − 0.0017 · n − 0.848
n
a 1 (n) = −0.0375 − 0.0185
n
a 2 (n) = −14.15 + 0.019 · n − 10.4
n
a 3 (n) = −105.64 + 0.019 · n − 58.52
n
Direct measurements of the [Siii] temperature have been possible with the availability of
the collisional lines in the near IR. The ratio is:
R S3 =
I(9069Å) + I(9532Å)
I(6312Å)
This expression can be simplified in case of lacking one of the near IR lines, using the
theoretical ratio I(9532Å) ≈ 2.44 · I(9069Å). The temperature can be calculated by the fit:
t([Siii]) = R S3 + 36.4
1.8 · R S3 − 3.01
B.2 Ionic abundances
The derived fittings to the ionic task results following the functional form given by Pagel
et al. (1992) for each element are listed below. In all relations t denotes the appropriate line
electron temperature, in units of 10 4 K, corresponding to the assumed ionization structure,
and n the electron density.