A VLT study of metal-rich extragalactic H II regions

I. Observations and empirical abundances

¹ Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu 96822, USA e-mail: bresolin@ifa.hawaii.edu
² Observatoire de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland e-mail: daniel.schaerer@obs.unige.ch
³ Laboratoire Astrophysique de Toulouse-Tarbes (UMR 5572), Observatoire Midi-Pyrénées, 14 avenue E. Belin, 31400 Toulouse, France
⁴ Instituto de Astrofísica de Andalucía (CSIC), Apdo. 3004, 18080 Granada, Spain e-mail: rosa@iaa.es
⁵ LUTH, Observatoire de Paris-Meudon, 5 place Jules Jansen, 92195 Meudon, France e-mail: grazyna.stasinska@obspm.fr

Received: 5 May 2005
Accepted: 3 June 2005

Abstract

We have obtained spectroscopic observations from 3600 Åto 9200 Åwith FORS at the Very Large Telescope for approximately 70 H iiregions located in the spiral galaxies NGC 1232, NGC 1365, NGC 2903, NGC 2997 and NGC 5236. These data are part of a project to measure the chemical abundances and characterize the massive stellar content of metal-rich extragalactic H iiregions. In this paper we describe our dataset, and present emission line fluxes for the whole sample. In 32 H iiregions we measure at least one of the following auroral lines: [S ii]4072, [N ii]5755, [S iii]6312 and [O ii]7325. From these we derive electron temperatures, as well as oxygen, nitrogen and sulphur abundances, using classical empirical methods (both so-called “T_e-based methods” and “strong line methods”). Under the assumption that the temperature does not introduce severe biases, we find that the most metal-rich nebulae with detected auroral lines are found at 12 + log(O/H)  8.9, i.e. about 60% larger than the adopted solar value. However, classical abundance determinations in metal-rich H iiregions may be severely biased and must be tested with realistic photoionization models. The spectroscopic observations presented in this paper will serve as a homogeneous and high-quality database for such purposes.