Resumen de Formation and dynamics of groups of galaxies in the local universe
Laura Darriba Pol
Galaxy groups are believed to play a key role in the formation and evolution of structure in the universe as they are the most common environment where galaxies reside. Despite its abundance, these galaxy aggregations have, however, received little attention in contrast to the more conspicuous and richer clusters of galaxies. At group scales, most efforts have been focused so far in investigating the evolutionary effects of the global tidal field in a fully assembled group environment. The goal of this PhD thesis is to examine the role played by the frequent low-speed galaxy collisions that occur during the pre-collapse phase of these systems in shaping the properties of the group members and the intragroup medium.
The first part of the work presents a fully functional numerical model of a pre-virialized galaxy group within the framework of the LambdaCDM concordance cosmology. This group model, which provides a realistic caricature of these systems in the early stages of their formation, is designed to extend the methodology of binary merger simulations to these scales. Both the group and its member galaxies are modeled as live multicomponent, collisionless, N-body systems, composed of dark matter and stars.
The second part of the thesis presents a series of results inferred from six high-resolution 10^7-particle simulations of our pre-virialized groups. All groups are evolved for about 10 Gyr and cover a relatively broad parameter space of initial conditions. We apply several measurement techniques and use different astronomical tools to study both the production of intergalactic luminous material (IGLM) and the evolution of galaxy properties driven by the frequent encounters experienced by galaxies in the group environment. By following the evolution of isolated binary mergers, from the binding energy and local density of the particles, we find momentary but significant decrements in the number of bound particles due to punctual kinematic decouplings of the dense galactic cores and a staggered evolution of the unbound mass. The results of this sort of analysis further indicate that the binding energy of the stripped starlight is essentially uncorrelated with the local mass density. We also characterize the structure and kinematics of two representative major mergers finding indications that the full relaxation of the outer radial structure of the remnants requires a minimum of ~ 2 Gyr. This however does not preclude that the fraction of diffuse stellar material of the remnants does not change significantly with time after the coalescence of the cores of the progenitors. Furthermore, we find that all our simulations produce systematically a low (< 10%) IGLM fraction. In the absence of a larger statistics that increases the confidence of our results, as well as of a robust and unambiguous methodology for the identification of the diffuse light component, this finding suggests that the extraordinary amounts of light detected in some well-known Hickson Compact Groups, such as HCG 79 and HCG 90, cannot be made exclusively from stellar material stripped out of their member galaxies. Finally, in agreement with theoretical predictions, our simulations confirm that the selective merging that takes place in unrelaxed poor groups can transform an initially Schechter-like stellar mass distribution function into a bimodal one.
