Abstracts Astronomy & Space Science

Dynamics and Shapes of Galaxies: Orbit Modeling of Triaxial Galaxies Hosting Supermassive Black Holes

by Matthew Eric Quenneville

Elliptical galaxies display a wide variety of photometric and kinematic features. Supermassive black holes are thought to lie in the centers of all elliptical galaxies, with masses that exhibit tight correlations with the masses and velocity dispersions of their hosts. Measurement of these correlations in the local universe underpin our understanding of the growth of supermassive black holes throughout cosmic time. These measurements can only be as precise as our measurements of the underlying supermassive black hole masses and host galaxy properties. The most massive ellipticals exhibit photometric and kinematic signatures of triaxiality. While axisymmetric dynamical modeling has been most prevalent over the past decades, triaxial orbit modeling allows models to capture the orbital complexity that the more general geometry allows. The limited number of direct tests of triaxial models have revealed biased shape recoveries and inconsistencies with axisymmetric models.This dissertation begins by addressing the inconsistency between axisymmetric and triaxial models. Starting from the most commonly used existing triaxial orbit code, the axisymmetric limit is approached in a careful manner in order to acheive consistent and stable results. An updated version of this code is introduced which is about twice as fast and does not suffer from the same spurious minima that have been observed in the literature. This version is applied to fast-rotating massive elliptical galaxy NGC 1453.I then proceed to the triaxial case. I demonstrate that the existing code uses kinematics that are incorrect, and describe several other improvements to the code and the way it is typically applied. A novel search strategy is used to explore the six dimensional parameter space more accurately and with far fewer expensive model evaluations than previously used grid based searches. This methodology is applied to obtain a simultaneous measurement of the triaxial shape, dark matter halo, stellar mass-to-light ratio, and central black hole mass of NGC 1453.Next, the updated code is validated against mock galaxy data. The code updates have dramatically improved the precision of the code. When used to measure the triaxial shape of a mock galaxy, the axis ratios $p$ and $q$ are recovered with far more accuracy and precision than would be suggested by any previously reported triaxial recovery tests.Finally, I turn from dynamical modeling to examining photometry of massive elliptical galaxies. I present new measurements of K-band total magnitudes and half-light radii for a volume limited sample of $\sim100$ galaxies. These new, more accurate values are used to study the scaling relations among massive ellipticals. The resulting relations are consistent with a picture in which massive ellipticals form through dissipationless mergers. As the relationship between total luminosity and velocity dispersion are found to be poorly fit by a single power law, this suggests that the $M_\mathrm{BH}-L$ relation is likely to be a better predictor of central black hole…