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

Appendix
C
Empirical calibrators
In this Appendix we list all the empirical metallicity calibrators used in this work, their
definitions and calibrations. For a review on some of the metallicity calibrators described here
and its uncertainties see Pérez-Montero and Díaz (2005) and Kewley and Ellison (2008).
The O 23 parameter
The O 23 parameter, also known as R 23 , was defined as:
O 23 ≡
[Oii] λ3727 + [Oiii] λ4959 + [Oiii] λ5007
Hβ
by Pagel et al. (1979). The major drawback to using O 23 is that is doubled valued with metallicity.
Three different regions can be distinguished: a lower branch in which O 23 increases with
increasing abundance, an upper branch in which the opposite occurs and a turnover region.
McGaugh (1991) produced a calibration based on theoretical models in which the ionization
is provide by stellar clusters of different metallicities, including a correction for ionization
parameter variations. In this work we used the analytic expressions for the McGaugh (1991)
lower an upper branches given in Kobulnicky et al. (1999):
12 + log(O/H) lower =12 − 4.944 + 0.767x + 0.602x 2 − y(0.29 + 0.332x − 0.331x 2 ),
12 + log(O/H) upper =12 − 2.939 − 0.2x − 0.237x 2 − 0.305x 3 − 0.0283x 4 −
− y(0.0047 − 0.0221x − 0.102x 2 − 0.0817x 3 − 0.00717x 4 )
169