Dynamical and chemical evolution of gas-rich dwarf galaxies |
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| Authors: | Simone Recchi Francesca Matteucci Annibale D'Ercole |
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| Institution: | Dipartimento di Astronomia, Universitàdi Trieste, Via G. B. Tiepolo 11, 34131 Trieste, Italy;SISSA/ISAS, Via Beirut 2-4, 34014 Trieste, Italy;Osservatorio Astronomico di Bologna, via Ranzani 1, 44127 Bologna, Italy |
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| Abstract: | We study the effect of a single, instantaneous starburst on the dynamical and chemical evolution of a gas-rich dwarf galaxy, the potential well of which is dominated by a dark matter halo. We follow the dynamical and chemical evolution of the interstellar medium (ISM) by means of an improved two-dimensional hydrodynamical code coupled with detailed chemical yields originating from type II SNe, type Ia SNe and single low- and intermediate-mass stars (IMS). In particular we follow the evolution of the abundances of H, He, C, N, O, Mg, Si and Fe. We find that for a galaxy resembling IZw18, a galactic wind develops as a consequence of the starburst and it carries out of the galaxy mostly the metal-enriched gas. In addition, we find that different metals are lost differentially in the sense that the elements produced by type Ia SNe are lost more efficiently than others. As a consequence of that, we predict larger α /Fe] ratios for the gas inside the galaxy than for the gas leaving the galaxy. A comparison of our predicted abundances of C, N, O and Si in the case of a burst occurring in a primordial gas shows a very good agreement with the observed abundances in IZw18 as long as the burst has an age of ～31 Myr and IMS produce some primary nitrogen. However, we cannot exclude that a previous burst of star formation had occurred in IZw18, especially if the pre-enrichment produced by the older burst was lower than Z =0.01 Z⊙. Finally, at variance with previous studies, we find that most of the metals reside in the cold gas phase already after a few Myr. This result is mainly caused by the assumed low SN II heating efficiency, and justifies the generally adopted homogeneous and instantaneous mixing of gas in chemical evolution models. |
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| Keywords: | hydrodynamics ISM: abundances ISM: bubbles galaxies: dwarf galaxies: individual: IZw18 |
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