Balmer jump temperature determination in a large sample of low-metallicity HII regions ^*,**,***

¹ Main Astronomical Observatory, Ukrainian National Academy of Sciences, Zabolotnoho 27, Kyiv 03680, Ukraine e-mail: guseva@mao.kiev.ua
² Instituto de Astrofísica de Andalucía, Apdo. 3004, 18080 Granada, Spain
³ Institute for Astrophysics, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany

Received: 19 July 2006
Accepted: 21 December 2006

Abstract

Aims.Continuing the systematic determination of the electron temperature of H ii regions using the Balmer and/or Paschen discontinuities by Guseva et al. (2006, ApJ, 644, 890) we focus here on 3.6 m ESO telescope observations of a large new sample of 69 H ii regions in 45 blue compact dwarf (BCD) galaxies. This data set spans a wide range in metallicity () and, combined with the sample of 47 H ii regions from Guseva et al. (2006), yields the largest spectroscopic data set ever used to derive the electron temperature in the H⁺ zone.

Methods.In the same way as in Guseva et al. (2006) we have used a Monte Carlo technique to vary free parameters and to calculate a series of model spectral energy distributions (SEDs) for each H ii region. The electron temperature in the H⁺ zones was derived from the best fitting synthetic and observed SEDs in the wavelength range ~3200–5100 Å, which includes the Balmer jump.

Results.On the base of the present large spectroscopic sample we find that in hot (T_e(H⁺)  11 000 K) H ii regions the temperature of the O²⁺ zone, determined from doubly ionised oxygen forbidden lines, does not differ statistically from the temperature of the H⁺ zone. Thus, we confirm and strengthen the finding by Guseva et al. (2006). We emphasize that due to a number of modelling assumptions and the observational uncertainties for individual objects, only a large, homogeneous sample, as the one used here, can enable a conclusive study of the relation between T_e(H⁺) and T_e(O iii).