INVESTIGADORES
HÄGELE Guillermo Federico
artículos
Título:
The temperature and ionization structure of the emitting gas in HII galaxies: implications for the accuracy of abundance determinations
Autor/es:
HÄGELE, GUILLERMO F.; PÉREZ-MONTERO, ENRIQUE; DÍAZ, ÁNGELES I.; TERLEVICH, ELENA; TERLEVICH, ROBERTO
Revista:
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Editorial:
WILEY-BLACKWELL PUBLISHING, INC
Referencias:
Año: 2006 vol. 372 p. 293 - 312
ISSN:
0035-8711
Resumen:
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 21st century technology. This
methodology requires the production and calibration of empirical
relations between the different line temperatures that should supersede
currently used ones based on very simple, and poorly tested,
photoionization model sequences.
As a first step to reach these goals, we have obtained simultaneous blue
to far red long-slit 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 catalogue using the INAOE Virtual
Observatory superserver. Our spectra cover the range from 3200 to
10500Å, including the Balmer jump, the [OII]λλ3727,
29Å lines, the [SIII]λλ9069, 9532Å doublet as
well as various weak auroral lines such as [OIII]λ4363Å and
[SIII]λ6312Å.
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 per cent. These accuracies are expected to
improve as better calibrations based on more precise measurements, both
on electron temperatures and densities, are produced.
We have compared our obtained spectra with those downloaded from the
SDSS DR3 finding a satisfactory agreement. The analysis of these spectra
yields values of line temperatures and elemental ionic and total
abundances which are in general agreement with those derived from the
WHT spectra, although for most quantities they can only be taken as
estimates since, due to the lack of direct measurements of the required
lines, theoretical models had to be used whose uncertainties are
impossible to quantify.
The ionization structure found for the observed objects from the
O+/O2+ and S+/S2+ ratios
points to high values of the ionizing radiation, as traced by the values
of the `softness parameter' η which is less than 1 for the three
objects. The use of line temperatures derived from T([OIII]) based on
current photoionization models yields for the two highest excitation
objects, much higher values of η which would imply lower ionizing
temperatures. This is, however, inconsistent with the ionization
structure as probed by the measured emission-line intensities.
Finally, we have measured the T(Bac) for the three observed objects and
derived temperature fluctuations. Only for one of the objects, the
temperature fluctuation is significant and could lead to higher oxygen
abundances by about 0.20dex.