A&A 470, 865-874 (2007)
The metallicity gradient of M 33: chemical abundances of H II regionsL. Magrini1, J. M. Vílchez2, A. Mampaso3, R. L. M. Corradi4, 3, and P. Leisy4, 3
1 INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
2 Instituto de Astrofísica de Andalucía (CSIC) Apartado de Correos 3004, 18080 Granada, Spain
3 Instituto de Astrofísica de Canarias, c. vía Láctea s/n, 38200 La Laguna, Tenerife, Canarias, Spain
4 Isaac Newton Group of Telescopes, Apartado de Correos 321, 38700 Santa Cruz de La Palma, Canarias, Spain
(Received 9 March 2007 / Accepted 10 May 2007)
Context. We present spectroscopic observations of a sample of 72 emission-line objects, including mainly H II regions, in the spiral galaxy M 33. Spectra were obtained with the multi-object, wide field spectrograph AF2/WYFFOS at the 4.2 m WHT telescope. Line intensities, extinction, and electron density were determined for the whole sample of objects.
Aims.The aim of the present work was to derive chemical and physical parameters of a set of H II regions, and from them the metallicity gradient.
Methods.Electron temperatures and chemical abundances were derived for the 14 H II regions where both [O II] and [O III] emission line fluxes were measured, including the electron temperature sensitive emission line [O III] 436.3 nm and in a few cases [N II] 575.5 nm. The ionization correction factor (ICF) method was used to derive the total chemical abundances.
Results.The presence of abundance gradients was inferred from the radial behaviour of several emission-line ratios, and accurately measured from chemical abundances directly derived in 14 H II regions. The oxygen abundances of our H II regions, located in the radial region from ~2 to ~7.2 kpc, gave an oxygen gradient -0.0540.011 dex kpc-1
Conclusions.The overall oxygen gradient for M 33 obtained using ours and previous oxygen determinations in a large number of H II regions with direct electron temperature determination as well as abundance in young stars presented a two slope shape: -0.19 dex kpc-1 for the central regions (R < 3 kpc), and -0.038 dex kpc-1 for the outer regions (R 3 kpc).
Key words: galaxies: abundances -- galaxies: evolution -- galaxies: individual: M 33 -- ISM: abundances -- ISM: HII regions
© ESO 2007