The prevailing model of structure formation that describes how matter is distributed throughout the Universe is known as the Lambda Cold Dark Matter paradigm. A key component of this paradigm is dark matter, which has so far gone undetected in laboratory experiments but is inferred from a wide variety of astrophysical observations. Although the Cold Dark Matter paradigm is extremely successful on large scales, there are significant differences between what computer simulations predict and what we observe on galaxy scales. The purpose of the work presented in this Dissertation is to address some of the issues surrounding the current structure formation paradigm and further develop some tools for investigating small scale structure. An issue that has caused recent controversy is known as the Planes of Dwarf Galaxies problem which describes the curious alignment of the Milky Way's dwarf galaxies into a thin planar structure. We have investigated this structure through time by integrating their orbits using the latest proper motion data as well as compared the distribution with current cosmological simulations and found no significant difference between the Milky Way distribution and simulations.

Through analysis of observations of the disturbances in the extended neutral hydrogen disks of spiral galaxies, one can characterize dark matter substructure and the dark matter halo of a host galaxy. This process is called Tidal Analysis. Using a simple test particle code to model satellite interactions with a gas disk, we have developed a scaling relation to relate the observed density response of the disk to the mass and pericenter of a satellite. With this relation, observers can now immediately infer the recent interaction history of a spiral galaxy from neutral hydrogen studies. Changing gears to observational studies of small scale structure, we report observations of Cepheid variables in a putative dwarf galaxy located along the line of sight of the galactic plane that was first predicted through the use of Tidal Analysis. Observations are still ongoing; however, preliminary results indicate that the Cepheids are part of structure that is moving independently of the Milky Way. Finally, in an effort to use Tidal Analysis on other galaxies to constrain substructure, we have begun a 21-cm radio observing campaign of a set of spiral galaxies at redshift z=0.1 to obtain their total mass in neutral hydrogen. This unique set of galaxies also act as strong gravitational lenses, thus allowing us to use both Tidal Analysis and gravitational lensing together for the first time. We report a secure detection and mass measurement for one of our sources and six upper mass limits.

Publication Date


Document Type


Student Type


Degree Name

Astrophysical Sciences and Technology (Ph.D.)

Department, Program, or Center

School of Physics and Astronomy (COS)


Sukanya Chakrabarti

Advisor/Committee Member

Margaret Bailey

Advisor/Committee Member

Eric Blackman


RIT – Main Campus