Dynamics of Prolate Galaxies

Elliptical galaxies can be triaxial or axisymmetric, the latter including oblate and prolate shapes. Among axisymmetric galaxies, the internal dynamics of oblate galaxies has been extensively studied, while prolate systems have received less attention and are still not as well understood. This thesis aims to contribute to filling this gap by providing a theoretical analysis of various dynamical properties of prolate systems through a comparison with their oblate counterparts. We restrict the analysis to ellipsoidally stratified models, as they provide a good description of elliptical galaxies, and we focus on two-integral systems (i.e., systems described by a distribution function which depends on the classical two integrals of motion). To carry out a physically meaningful comparison between oblate and prolate galaxies, we construct oblate-prolate “conjugate pairs” with the same mass, intrinsic density profile and edge-on surface brightness. The possibility of constructing such photometrically identical systems is non-trivial and represents an important result of this work. The first step is therefore to identify the conditions to construct such conjugate pairs. We then explore more general differences between oblate and prolate galaxies. First, we use the Tensor Virial Theorem to study their main energetic differences. Second, we analyse their gravitational field and introduce the Jeans equations for two-integral systems. Third, we investigate the consistency of axisymmetric models by studying the sign of the average v_φ^2. Finally, we return to conjugate pairs to highlight kinematical differences and derive constraints on their intrinsic shape. The results of this thesis reveal the main peculiarities of prolate systems and show that they are not simply oblate systems with “inverted” axial ratio. Furthermore, by providing a clearer understanding of their dynamics, this work lays a solid foundation for future studies aimed at further exploring prolate galaxies.