Star formation and bar instability in cosmological halos

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Context. This is the third in a series of papers presenting the first attempt to analyse the growth of the bar instability in a consistent cosmological scenario. In the previous two articles, we explored the role of the cosmology on stellar disks and the impact of the gaseous component on a disk embedded in a cosmological dark matter halo. Aims. The aim of this paper is to point out the impact of the star formation on the bar instability inside disks having different gas fractions. Methods. We performed cosmological simulations of the same disk-to-halo mass systems as in the previous works where the star formation was not triggered. We compared the results of the new simulations with the previous ones to investigate the effect of the star formation by analysing the morphology of the stellar components, the bar strength, the behaviour of the pattern speed. We followed the gas and the central mass concentration during the evolution and their impact on the bar strength. Results. A stellar bar, lasting 10 Gyr, is still living at z = 0 in all our cosmological simulations. The central mass concentration of gas and of the new stars has a mild effect on the ellipticity of the bar but is not able to destroy it, and at z = 0 the stellar bar strength is enhanced by the star formation. The bar pattern speed decreases with the disk evolution.