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Abstract: Star formation depends strongly both on the local environment of galaxies,and on the internal dynamics of the interstellar medium. To disentangle the twoeffects, we obtained, in the framework of the AMIGA project, Ha and Gunn rphotometric data for more than 200 spiral galaxies lying in very low-densityregions of the local Universe. We characterise the Ha emission, tracing currentstar formation, of the 45 largest and less inclined galaxies observed for whichwe estimate the torques between the gas and the bulk of the optical matter. Wecould subsequently study the Ha morphological aspect of these isolated spiralgalaxies. Using Fourier analysis, we focus on the modes of the spiral arms andalso on the strength of the bars, computing the torques between the gas andnewly formed stars Ha and the bulk of the optical matter Gunn r. Weinterpret the various bar-spiral morphologies observed in terms of the secularevolution experienced by galaxies in isolation. We also classify the differentspatial distributions of star forming regions in barred galaxies. The observedfrequency of particular patterns brings constraints on the lifetime of thevarious evolution phases. We propose an evolutive sequence accounting for thetransitions between the different phases we could observe. Isolated galaxiesappear not to be preferentially barred or unbarred. Through numericalsimulations, trying to fit the Ha distributions yields constraints on the starformation law, which is likely to differ from a genuine Schmidt law. Inparticular, it is probable that the relative velocity of the gas in the baralso needs to be taken into account.



Author: S. Verley, F. Combes, L. Verdes-Montenegro, G. Bergond, S. Leon

Source: https://arxiv.org/



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