Dynamical structure and evolution of merger remnants

Abstract

From the most massive stellar systems known to be the end products of mergers, such as early-type galaxies, to the less massive ones, such as nuclear star clusters, the recent improvements of integral-field-unit (IFU) spectroscopic surveys have revealed that their stellar dynamics are much more complex than previously thought. These new insights are expected to reflect the complex assembly and evolutionary processes that create them and are now pointing to the need for more realistic scenarios for their formation. In the first part of this thesis, we study the connection between the present-day dynamical structure and the formation history of merger remnant early-type galaxies, by using mock observations extracted from merger simulations. We find that major mergers can account for the peculiar kinematic features that are often observed in early-type galaxies, such as kinematically decoupled cores, or prolate (long axis) rotation. We find a new channel for the formation of kinematically decoupled cores, that can help towards explaining their observed prevalence in IFU surveys. Additionally, we present the discovery of prolate rotation in nine early-type galaxies from the CALIFA IFU Survey, adding a significant fraction to the observed cases of such galaxies that exist so far in the literature. We show that prolate rotators can be the end-products of major mergers. In the second part, we address the role of mergers in the formation of Nuclear Star Clusters (NSCs), using simulations of consecutive infalls of globular clusters into the center of a galaxy. We find that NSCs resulting from this process show both morphological and kinematic properties that match the Milky Way NSC very well, including significant stellar rotation – a fact that has been attributed to gas infall so far. In general, our results demonstrate that mergers can account for a variety of observed kinematic features in both early-type galaxies and NSCs and place constraints on the role of mergers in their complex assembly history.