Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005a%26a...437..837d&link_type=abstract
Astronomy and Astrophysics, Volume 437, Issue 3, July III 2005, pp.837-847
Astronomy and Astrophysics
Astrophysics
7
Galaxies: Abundances, Ism: Abundances, Galaxies: Evolution, Galaxies General, Ism: H Ii Regions
Scientific paper
We used photoionization models in order to reproduce the observed gradients of emission-line ratios for 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_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_eff gradient of triangle T_eff/triangle R = (400 ± 112) K kpc-1 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.
Copetti Marcus V. F.
Dors L.. Jr. O.
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