Title: Stellar Streams, Dwarf Galaxy Pairs, and the Halos in which they Reside
Description: In this Dissertation we explore how the nature of tidal interactions tear gravitationally bound systems apart into distinct morphological and kinematic structures. We use the properties of these structures, persisting for billions of years, to investigate the potential of the Milky Way Galaxy and to disentangle the baryonic evolution of gas in dwarf galaxy interactions. We approach these problems through a combination of observations, and simulations, as well as comparisons between the two. In particular, we use the properties of the thin, curved stellar stream emerging from the old, Milky Way globular cluster, Palomar 5 (Pal 5) to show that its mere existence can rule out a moderately triaxial potential model of our Galaxy. Pal 5-like streams on appropriate orbits diffuse much further in space from the orbital path (dubbed “stream-fanning”) in this triaxial potential than in the oblate case. We further show that torques from the Milky Way’s Galactic bar, can create ever-widening gaps in stellar streams.

The fact that the bar can create such under densities, demonstrates that we should be careful when interpreting gaps in stellar streams as indirect evidence of the existence of dark matter subhalos in our Galaxy. We carry out a systematic study of resolved neutral hydrogen (HI) synthesis maps of 10 interacting dwarf galaxy pairs. The pairs are located in a range of environments and captured at various interaction stages. We find that the neutral gas is extended in the interacting pairs when compared to non-paired analogs, indicating that gas is tidally pre- processed. Additionally, we find that dwarf-dwarf interactions enable the “parking” of gas at large distances to serve as a continual gas supply channel to the dwarfs until accretion by a more massive host. We model a specific dwarf pair in our sample, NGC 4490/85, which is an isolated analog of the Magellanic Clouds and is surrounded by a ∼50 kpc extended HI envelope. We use hybrid N-body and test-particle simulations along with a visualization interface to simultaneously reproduce the observed present-day morphology and kinematics.

Our numerical results con- firm that encounters between two dwarf galaxies can “park” baryons at very large distances, without the aid of environmental effects. The extended tidal features will continue to evolve over several billion years which will affect the efficiency of gas stripping if such dwarf pairs are accreted by a massive host. In contrast, in isolated environments dwarf-dwarf interactions can create a long-lived supply mode of gas to the merger remnant potentially explaining the population of dwarfs in the field with large gas envelopes, but limited star formation. All of these topics share the common theme of utilizing morphological and kinematic structures left behind from ongoing gravitational interactions on various scales.