Formation & Evolution of early-types galaxies : Numerical simulations of galaxy mergers

• Main Author: Bois, Maxime
• Language: FRE
• Published: Université Claude Bernard - Lyon I 2011
• Subjects: [SDU:OTHER] Sciences of the Universe/Other; Formation and evolution of galaxies; Early-type galaxies; Numerical simulation
• Online Access: http://tel.archives-ouvertes.fr/tel-00845753; http://tel.archives-ouvertes.fr/docs/00/84/57/53/PDF/TH2011_Bois_Maxime2.pdf

A simple morphological classification of the galaxies in the local Universe shows two main families: (1) the disc galaxies, with spiral arms and in two-thirds of these galaxies a stellar bar; and (2) the elliptical and lenticular galaxies, labelled early-type galaxies (ETGs), which are dominated by a spheroidal stellar component. ETGs are among the most massive galaxies of the local Universe and present a red color, meaning that their stars are old. These galaxies also present a large diversity of stellar dynamics: they may have a regular rotation pattern aligned with the photometry or perpendicular to it; they can present no global rotation at all; or may hold a central stellar component with a rotation axis distinct from the outer stellar body called a Kinematically Distinct Core (KDC). These features observed in the dynamics of the ETGs and their large mass are clearly signs of past interactions, especially signs of galaxy mergers. The main goal of my thesis is to analyse a large sample of high-resolution numerical simulations of binary galaxy mergers. These binary mergers are called "idealized" because they do not take into account the full cosmological context of galaxy formation: two isolated spiral galaxies are launched in an orbit resulting in a merger of the galaxies, the final remnant is an ETG. The statistical analysis of this large sample of simulations enables us to link the initial conditions of the merger to the final merger remnant. I demonstrated that the mass ratio between the spiral progenitors and the orientation of their spins of angular momentum are the main drivers for the formation of fast and slow rotating ETGs and the KDCs. The morphology of the initial spiral (Bulge/Disc ratio) seems also to play a major role for the formation of the different types of ETGs but its impact is not completelly clear, and other simulations are planned to clarify this problem. During my thesis, I also studied the importance of the resolution in the numerical simulations of galaxy mergers. I showed that the number of particles and the size of the computational grid have a predominant role in the final product of the merger. A too low resolution (i.e. too few particles and a coarse grid) can not follow the rapid evolution of the gravitational potential during the merger. In this case, the angular momentum is not as efficiently transfered to the outer parts of the galaxy: the merger remnant keeps thus a strong and regular rotation. At higher resolution, the scattering of the orbit is resolved and the merger remnant may end-up with, under some special initial conditions, a slow rotation and may form a KDC.