CHEMICAL GRADIENTS OF ABUNDÂNCIAS IN GALAXIES SPIRALS

We used photoionization models in order to derive O/H, N/O, and S/O abundance gradients in three isolated barred spiral galaxies (NGC 1365, NGC 925, NGC 1073) and in nine spiral galaxies (NGC 4501, NGC 4571, NGC 4689, NGC 4254, NGC4321, NGC4654, NGC4303, NGC4651, NGC4713) in the Virgo cluster. 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 measures. For NGC 1365, our models indicate no abundance break, result suggested in previous works. ln NGC 925, despite the flattening in the R23 = ([O Il].\3727+[0 IlI].\4949+.\5007)/H,B oxygen indicator at galactocentric distances R >6.0 kpc, our model results did not show any presence of an oxygen abundance break. 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 gradient for the ionizing star temperatures of the nebulae Teff of L:.Teff /6R = (400 ::I:: 112) K kpc -1 and the logarithmic of the ionizing parameter log U ranging from -3.0 to -2.3. The N/O vs. O/H diagram derived from our results for isolated galaxies is in general 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 abundances was found. Our models indicate that galaxies near to the core ofthe Virgo cluster are overabundant in O/H, N/O, and S/O by about 0.25 dex in comparison to the ones at the periphery. With one exception, models with upper stellar mass limit of Mu= 30-40 M0 and age of the ionizing star cluster ranging from 1.5 to 2.5 Myr were able to reproduce the observational data. Chemical evolution models indicate that the collapse time-scale for the inner regions of the galaxies near to the Virgo core is larger than the one in galaxies located at the intermediate and peripheral positions in the cluster, what can be due to the dense environment existing in the Virgo cluster core.%%%%Nos usamos modelos de fotoionizacao com o objetivo de derivar gradientes de abundâncias de O/H, N/O e S/O em tres galaxias espirais barradas isoladas (NGC 1365, NGC 925, NGC 1073) e em nove galaxias espirais (NGC 4501, NGC 4571, NGC4689, NGC4254, NGC4321, NGC4654, NGC4303, NGC4651, NGC4713) no aglomerado de Virgem. Nossas predicoes para O/H mostraram-se consistentes com algumas determinacoes de abundância empiricas, mas elas estao superestimadas por um fator de 0.1-004 dex quando comparadas a medidas diretas de abundâncias. Para NGC 1365, nossos modelos nao indicaram nenhuma quebra de gradientes, resultado sugerido por trabalhos anteriores. Em NGC 925, apesar do valor constante do indicador de oxigenio R23 = ([O II]A3727+[0 III]A4949+A5007)/H,B para distâncias galactocentricas R >6.0 kpc, nossos modelos nao mostraram nenhuma presenca de quebra nos gradientes de abundâncias. NGC 1073 parece ser superabundante em nitrogenio comparada a outras…