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Astron. Astrophys. 337, 338-348 (1998)

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5. Summary

In this paper we attempted to model the chemical evolution of dwarf irregulars and blue compact galaxies. In particular, we considered the presence of dark matter halos and of the different contributions to the interstellar gas energy due to supernovae (II and Ia) and stellar winds from massive stars. The comparison with the available data on the abundances and abundance ratios of elements such as He, N, C, O, and Fe allowed us to conclude that DIG and BCG must contain a substantial amount of dark matter in order to be gravitationally bound against the intense starbursts, that galactic winds powered by supernovae and stellar winds from massive stars are preferably enriched (differential), and that the energy contribution from type Ia supernovae to the total thermal energy of the gas is negligible relative to the type II supernova component. We found also that the stellar wind contribution is negligible relative to that of the type II supernovae.

In summary, our models suggest:

  • a number of bursts [FORMULA];

  • a star formation efficiency [FORMULA];

  • differential galactic winds mostly powered by supernovae of type II, with a wind efficiency parameter [FORMULA];

  • a ratio between dark matter and luminous matter [FORMULA]; in particular, for one or two bursts models we find [FORMULA] whereas for multi-burst models (up to 7) [FORMULA] is required.

  • a dark matter distribution given by the ratio between luminous effective radius and dark effective radius [FORMULA];

  • Salpeter IMF is favoured relative to Scalo IMF: in fact the observed abundance ratios are better reproduced by Salpeter models than by Scalo models, in particular the spread of N/O abundance ratio.

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© European Southern Observatory (ESO) 1998

Online publication: August 17, 1998