Comparative internal kinematics of the H II regions in interacting and isolated galaxies: Implications for massive star formation modes

We have observed 12 interacting galaxy pairs using the Fabry-Perot interferometer GH αFaS (GalaxyHα Fabry-Perot system) on the 4.2-mWilliam Herschel Telescope at theObservatorio del Roque de los Muchachos, La Palma. We present here the Hα surface brightness, velocity and velocity dispersion maps for the 10 systems we have not previously observed using this technique, as well as the physical properties (sizes, Hα luminosities and velocity dispersion) of 1259 HII regions from the full sample. We also derive the physical properties of 1054 HII regions in a sample of 28 isolated galaxies observed with the same instrument in order to compare the two populations of HII regions. We find a population of the brightest HII regions for which the scaling relations, for example the relation between the Hα luminosity and the radius, are clearly distinct from the relations for the regions of lower luminosity. The regions in this bright population are more frequent in the interacting galaxies. We find that the turbulence, and also the star formation rate (SFR), are enhanced in the HII regions in the interacting galaxies. We have also extracted the Hα equivalent widths for the HII regions of both samples, and we have found that the distribution of HII region ages coincides for the two samples of galaxies. We suggest that the SFR enhancement is brought about by gas flows induced by the interactions, which give rise to gravitationally bound gas clouds which grow further by accretion from the flowing gas, producing conditions favourable to star formation. Key words: stars: formation -HII regions - galaxies: interactions - galaxies: ISM- galaxies: kinematics and dynamics