The metallicity gradient of M 33: chemical abundances of H ii regions

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 den...

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Bibliographic Details
Published in:Astronomy and astrophysics (Berlin) 2007-08, Vol.470 (3), p.865-874
Main Authors: Magrini, L., Vílchez, J. M., Mampaso, A., Corradi, R. L. M., Leisy, P.
Format: Article
Language:English
Subjects:
Astronomy
Earth, ocean, space
Exact sciences and technology
galaxies: abundances
galaxies: evolution
galaxies: individual: M 33
ISM: abundances
ISM: HII regions
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Summary: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 -0.054±0.011 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).
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361:20077445