Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt.........5z&link_type=abstract
PhD Dissertation, Columbia Univ. Dobbs Ferry, NY United States
Astronomy and Astrophysics
Astronomy
17
Galactic Bulge, Galactic Nuclei, Stellar Mass, Stellar Models, Line Of Sight, Ellipsoids, Astronomical Models, Retrograde Orbits, Rotating Bodies, Velocity Distribution, Three Dimensional Models, Quadratic Programming
Scientific paper
In this thesis, I present dymamical models for the Galactic bar. Chapter 1 summarizes the current observations of the shape and dynamics of the Galactic bulge/bar. While clear evidence for a triaxial bulge has been seen in the star count data, integrated light distribution and gas kinematics, there is a paucity of stellar kinematic evidence of the bar. I also note the general lack of self-consistent bar models in the literature, which severely limit our ability to interpret the observations. In Chapter 2, I present the first clear stellar kinematic evidence for vertex deviation, a 'smoking gun' of bulge triaxiality, based on the Baade's Window data. In the analysis we develop a robust technique in interpreting kinematics and abundance data. Our results argue that orbit families correlate with metallicities of stars and the bulge/bar forms dissipatively. In Chapter 3, I present a self-consistent stellar dynamical model for the bar of our Galaxy constructed from numerically computed orbits. The model fits the density profile of the COBE light distribution, the observed solid body stellar rotation curve, the fall-off of minor axis velocity dispersion and the velocity ellipsoid at Baade's Window. The fully self-consistent model was constructed using quadratic programming to assign weights to 1000 orbits running in a rotating bar potential. This model is the first self-consistent rapidly rotating 3D bar model built using an extension of Schwarzschild's orbit technique. The bar is smooth in phase space with the direct boxy orbits being the dominant orbit family; there are approximately 20% retrograde orbits in the model. I have explored the range of models consistent with current data and suggest future observations that will distiguish between models. These techniques can be easily applied to external bulges and galactic nuclei. We use the self-consistent bar to build a microlensing model for the Galactic Bulge in Chapter 4. Comparing with the OGLE observations, we find that the observed large optical depth and long microlensing event duration towards the Bulge are consistent with a 2 x 1010 solar mass bar elongated along our line-of-sight and with lenses being ordinary stars of mass greater than 0.1 solar mass; the model predicts 5-7 events with typical time scale of 20 days for the OGLE. The thesis results also include finding a very general family of analytical density-potential pairs for bulges and nuclei of general shape and radial profile (Chapter 5). Most of the well-known spherical density-potential pairs are special cases of this generalization, including the eta-models, the Plummer model, the Perfect Sphere model, and the modified Hubble profile. We demonstrate its application to study dynamics of both spherical and non-spherical systems.
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