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

162 Appendix B
where
R S2 = I(6717Å)
I(6731Å)
R S2 is related with the density in the following way:
n([Sii]) = 10 3 · RS2 · a 0 (t) + a 1 (t)
R S2 · b 0 (t) + b 1 (t)
a 0 (t) = 2.21 − 1.3/t − 1.25t + 0.23t 2
a 1 (t) = −3.35 + 1.94/t + 1.93t − 0.36t 2
b 0 (t) = −4.33 + 2.33/t + 2.72t − 0.57t 2
b 1 (t) = 1.84 − 1/t − 1.14t + 0.24t 2
here t is generally t([Oiii]), where t = 10 −4 T e , although an iterative process could be used to
calculate it with t([Sii]) given that this temperature, like t([Oii]), a type np 3 ion, is density
dependent.
Oxygen
In the case that enough spectral resolution is available to resolve the [Oii] doublet, we
can use the ratio:
where
R ′ O2 = I(3727Å)
I(3729Å)
Therefore, the density can be calculated through the expression:
n([Oii]) = 10 2 · R′ O2 · a 0(t) + a 1 (t)
R ′ O2 · b 0(t) + b 1 (t)
a 0 (t) = 4.99 + 7.12/t − 4.71t
a 1 (t) = −3.69 − 4.54/t + 3.27t
b 0 (t) = 0.29 − 0.52/t − 0.011t
b 1 (t) = −0.88 + 1.85/t − 0.052t
where t can be t([Oiii]), although an iterative process can be used to calculate it by means
of t([Oii]).