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

B • Physical conditions of the gas and abundances 163
B.1.2 Temperature
The following expressions are valid in the temperature range between 7000 and 23000 K
and the errors involved in the fit are always lower than observational errors by factors between
5 and 10.
Oxygen
[Oiii] temperature is calculated from the ratio:
R O3 =
I(4959Å) + I(5007Å)
I(4363Å)
The fit, as for the rest of the np 2 ions, is independent of the electron density:
t([Oiii]) = 0.8254 − 0.0002415 R O3 + 47.77
R O3
For [Oii] the ratio for the electron temperature is calculated from:
R O2 =
I(3727Å) + I(3729Å)
I(7319Å) + I(7330Å)
The [Oii] λλ 7319,7330 Å lines have a contribution from direct recombination which increases
with temperature. Such emission, however, can be quantified and corrected for as:
I R (7319 + 7330)
I(Hβ)
0.44 O2+
= 9.36 t
H +
where t denotes the electron temperature in units of 10 4 K (Liu et al., 2000). This expression
is valid only in the range of temperatures between 5000 and 10000 K.
The ratio of the [Oii] lines depends on the electron density:
where the coefficients are respectively:
t([Oii]) = a 0 (n) + a 1 (n) · R O2 + a 2(n)
R O2
a 0 (n) = 0.23 − 0.0005 · n − 0.17
n
a 1 (n) = 0.0017 − 0.000009 · n − 0.0064
n
a 2 (n) = 38.3 − 0.021 · n − 16.4
n