The temperature and ionization structure of the emitting gas in HII galaxies: Implications for the accuracy of abundance determinations

Abstract

We propose a methodology to perform a self-consistent analysis of the physical properties of the emitting gas of HII galaxies adequate to the data that can be obtained with the XXI century technology. This methodology requires the production and calibration of empirical relations between the different line temperatures that should superseed currently used ones based on very simple, and poorly tested, photo-ionization model sequences. As a first step to reach these goals we have obtained simultaneous blue to far red longslit spectra with the William Herschel Telescope (WHT) of three compact HII galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 2 (DR2) spectral catalog using the INAOE Virtual Observatory superserver. Our spectra cover the range from 3200 to 10500 Å, including the Balmer jump, the [OII]3727,29 Ålines, the [SIII]9069,9532 Ådoublet as well as various weak auroral lines such as [OIII]4363 Åand [SIII]6312 Å. For the three objects we have measured at least four line temperatures: T([OIII]), T([SIII]), T([OII]) and T([SII]) and the Balmer continuum temperature T(Bac). These measurements and a careful and realistic treatment of the observational errors yield total oxygen abundances with accuracies between 5 and 9%. These accuracies are expected to improve as better calibrations based on more precise measurements, both on electron temperatures and densities, are produced. ...