Continuous star formation in IZw18

¹ Institut für theoretische Physik und Astrophysik, Kiel University, Olshausenstrasse 40, 24118 Kiel, Germany e-mail: recchi@mpa-garching.mpg.de
² Max-Planck Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85741 Garching bei München, Germany
³ Dipartimento di Astronomia, Università di Trieste, Via GB Tiepolo, 11, 34131 Trieste, Italy e-mail: matteucci@ts.astro.it
⁴ INAF - Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127 Bologna, Italy e-mail: [annibale;tosi]@bo.astro.it

Received: 27 March 2004
Accepted: 25 May 2004

Abstract

We study the dynamical and chemical evolution of a galaxy similar to IZw18 under the assumption of a continuous star formation during bursts. We adopt a 2-D hydrocode coupled with detailed chemical yields originating from SNeII, SNeIa and from single intermediate-mass stars. Different nucleosynthetic yields and different IMF slopes are tested. In most of the explored cases, a galactic wind develops, mostly carrying out of the galaxy the metal-enriched gas produced by the burst itself. The chemical species with the largest escape probabilities are Fe and N. Consequently, we predict that the [ α/Fe] and [ α/N]  ratios outside the galaxy are lower than inside. In order to reproduce the chemical composition of IZw18, the best choice seems to be the adoption of the yields of Meynet & Maeder ([CITE]) which take into account stellar rotation, although these authors do not follow the whole evolution of all the stars. Models with a flat IMF () seem to be able to better reproduce the chemical properties of IZw18, but they inject in the gas a much larger amount of energy and the resulting galactic wind is very strong, at variance with observations. We also predict the evolution of the abundances in the H i medium and compare them with recent FUSE observations.