Dynamics of merging galaxieskey steps in the evolution of galaxies

Resumen

We present in this thesis a study of the kinematics of the ionized gas in 12 interacting galaxies using observations made with a Fabry-Perot interferometer, and a study of the kinematics of the molecular gas in one of the systems of our sample using observations taken with a radiointerferometer. We study the interacting galaxy pair Arp 270 which shows distorted kinematics but whose rotation is sufficiently coherent that we can separate out the non-circular motion. We detect an inflow of gas towards the nucleus induced by the interaction, as well as an almost perpendicular biconical outflow of gas from the nucleus. We identify and measure the parameters (luminosity, radius, and velocity dispersion) of the HII regions. We find that the more luminous HII regions have densities which increase with mass, and that these regions are clearly induced by the interaction. We also present a study of the "Antennae", a pair of merging galaxies which is more complex than Arp 270 but has been widely studied in the literature. It is generally accepted that the Antennae will become an ultraluminous infrared galaxy (ULIRG) as it evolves. For this reason studying the Antennae gives us important clues about the formation of massive galaxies in general. We find in the Antennae the same dichotomy between less luminous and more luminous HII regions as we found in Arp 270. In fact we were able to make a comparison between the HII region parameters and those of the giant molecular clouds (GMC's) using ALMA observations, and we have found a link between the two populations of HII regions and two populations of GMC's. The surface density of a GMC rises with radius (and mass) a result which differs from what has been observed in previous studies of non-interacting galaxies. As a result the star formation rate is higher in the more massive star forming regions. To deepen our study of the kinematics of interacting galaxies we made a comparison between the HII regions of our sample of 12 interacting pairs and a sample of 28 non-interacting galaxies observed with the same Fabry-Perot interferometer. We identified and measured the parameters of 1336 HII regions in the sample of interacting galaxies, and of 1118 HII regions in the sample of non-interacting galaxies. We find that the more luminous HII regions, those where the gas density rises with increasing mass, are considerably more common in the sample of interacting galaxies and that this gives rise to higher star formation rates in the interacting sample. The spectral dimension of the data cubes allows us to make a comparison between the kinetic energy and the gravitational energy of the star forming regions. The result is that the more massive regions are gravitationally bound while the less massive regions are pressure bounded. The rise in the star formation rate in interacting galaxies which are undergoing a merger should leave traces in the evolution of galaxies in earlier epochs when the merger rates were higher, since the Initial Mass Function is almost certainly dependent on the star formation rate, which in turn depends on the parameters of the placental molecular clouds as found in their scaling relations.