Structure and Stability of Cuspy Triaxial Galaxies

University Of Florida, Gainesville FL

Investigators

Abstract

AST-0070809 Kandrup, Henry E. Structure and Stability of Cuspy Triaxial Galaxies The goal of this project is to construct triaxial distribution functions (DFs) for cuspy elliptical galaxies and early-type bulges. This will involve the integration of techniques from classical celestial mechanics, modern nonlinear dynamics and statistical mechanics, as well as numerical algorithms, such as modifications to Schwartzschild's technique for DF construction. It aims to answer the question: What is the connection between the DF and the surface density profiles in triaxial galaxies, and what is the influence of chaos in this connection or are the surface density profiles relics of initial conditions? Recent high resolution observations indicate that many (perhaps most) elliptical galaxies have a pronounced density cusp, possibly associated with the presence of a supermassive black hole; in addition, for galaxies where the cusp is not too steep, there is often evidence for moderate deviations from axisymmetry. However, theoretical arguments, corroborated by numerical investigations, suggest strongly that many of the stars in a cuspy, nonaxisymetric galaxy will exhibit chaotic motions. Until very recently, almost all work in this area has completely ignored the possible effects of this chaos. This project will explore the physical implications of this chaos on the structure and evolution of galaxies, with particular focus on determining potentially observable signatures. Questions to be addressed include the following: 1. Is it reasonable to model such galaxies as being in a time-independent statistical equilibrium, or would one anticipate that cuspy nonaxisymmetric galaxies should exhibit systematic evolutionary effects over astronomically interesting time scales? 2. How susceptible are such galaxies towards low amplitude gravitational irregularities associated with the presence of other comparatively nearby galaxies? 3. How will such a galaxy respond to a collision or close encounter with a very nearby galaxy? Much of this work involves applications of ideas which have been developed by physicists and applied mathematicians over the past thirty years and which have been confirmed repeatedly in the laboratory. However, an important new feature arising in the context of galaxies is that the chaos is generated self-consistently: In most laboratory experiments, chaos is triggered by some external stimulus acting on the system being probed. When considering a galaxy one is confronted with a situation where the chaos is induced by the gravity associated with the matter in the galaxy itself. Funding for this project is provided by the NSF program for Extragalactic Astronomy & Cosmology (AST/EXC). ***