Astronomy & Astrophysics

Free access article

Issue		A&A Volume 437, Number 3, July III 2005
Page(s)		837 - 847
Section		Extragalactic astronomy
DOI		10.1051/0004-6361:20040219

A&A 437, 837-847 (2005)
DOI: 10.1051/0004-6361:20040219

Abundance gradients in a sample of barred spiral galaxies

O. L. Dors Jr. and M. V. F. Copetti

Laboratório de Análise Numérica e Astrofísica, Departamento de Matemática, Universidade Federal de Santa Maria, 97119-900 Santa Maria, RS, Brazil
e-mail: oli@lana.ccne.ufsm.br

(Received 6 February 2004 / Accepted 14 March 2005 )

Abstract
We used photoionization models in order to reproduce the observed gradients of emission-line ratios for $\ion{H}{ii}$ regions located in the normal spiral galaxy M 101 and in three barred spiral galaxies, namely NGC 1365 , NGC 925 , and NGC 1073 . The behavior of the following nebular parameters across the disk of these galaxies was determined: temperature of the ionizing star ( $T_{\rm eff}$ ), ionization parameter (U), and the abundance ratios O/H, N/O, and S/O. Our O/H predictions were found to be consistent with some empirical abundance determinations, but are overestimated by a factor of 0.1-0.4 dex when compared to the direct abundance determinations. NGC 1073 seems to be overabundant in nitrogen compared to other spiral galaxies. No gradient of S/O was found in the studied galaxies, and we derived a positive $T_{\rm eff}$ gradient of $\triangle T_{\rm eff}/\triangle R = (400 \pm 112)$ K $\rm kpc^$ and U ranging from -3.0 to -2.3. The N/O vs. O/H diagram in general is consistent with chemical evolution models that assume that the nitrogen synthesis has both a primary and a secondary component compared to oxygen. However, a very strong N/O dependence on the O/H at high abundance was found.

Key words: galaxies: abundances -- ISM: abundances -- galaxies: evolution -- galaxies general -- ISM: $\ion{H}{ii}$ regions

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