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Karl, Simon (2012): The Antennae Galaxies: a key to galactic evolution. Dissertation, LMU München: Fakultät für Physik



The Antennae galaxies (NGC 4038/39) are the nearest and best-studied major merger of two gas-rich spirals in the local Universe. They are named after the characteristic pair of tidal tails that protrude out of their main galactic disks. Due to their proximity the Antennae are extremely well sampled by modern high-resolution observations over an enormous wavelength range, from radio to X-ray. This allows for a comprehensive multiwavelength approach to the present-day morphology and dynamical history of the system. The goal of this Thesis is to test the available high-quality multiwavelength data against new high-resolution merger simulations as a key to improve our understanding of several merger-induced physical processes, such as starbursts and the formation of young star clusters. These processes are expected to have been even more important in the formation and early evolution of galaxies. First of all, accurate initial conditions for the interaction orbit and the initial galaxy models need to be constrained. To this end, we perform an extended parameter search in order to obtain a suitable match to the Antennae galaxies. Using these new initial conditions, we are able to present the first high-resolution numerical simulations that successfully match the detailed large- and small-scale morphology and kinematics of the Antennae galaxies. Moreover, the spatial distribution of star-forming regions as well as the total star formation rate are reproduced in excellent quantitative agreement, in particular, if we adopt a very weak stellar feedback. We find that the Antennae are currently in a special phase of their evolution, shortly after the second pericenter. They will merge soon within the next ~50 Myr. In addition, we compare the star formation histories of all published hydrodynamical Antennae simulations with the observed cluster age distribution. The latter is well approximated by a power-law dN/dt ~ t^gamma, declining as gamma = 1. Under the assumption that clusters form at rates proportional to the total star formation, it is found that the variations in the simulated formation histories alone cannot account for most of the steep decline in the observed age distribution. This provides strong evidence for efficient, prolonged cluster disruption in the Antennae, similar to more quiescent galaxies. Finally, we address the question of whether the Antennae will evolve into a typical elliptical galaxy. We find that the virialized merger remnant resembles an oblate, fast-rotating early-type with surface brightness profile well fitted by a Sersic function of index n ~ 5. For high metallicities (Z > Z_sun) the stellar remnant of the Antennae may add to a population of present-day ellipticals after secular evolution of another ~2.5 -3 Gyr. Within this Thesis, we present an improved numerical model for the interacting Antennae galaxies that may serve as a test-bed for further investigations of this archetypal merger. As next steps, we plan to investigate the extended hot gas component found in X-ray observations of the Antennae, and test our present results in a code comparison project.