Abstract
The nature of dark matter remains a mystery which has yet to be solved. Although a dark matter
particle has yet to be detected, its gravitational effect on visible matter can be measured on large
scales with structures such as stellar streams, the elongated remnants of tidally stripped dwarf
galaxies and globular clusters, which have proven to be formidable tools for indirectly investigating
dark matter within our own Milky Way. While they have revealed much about the structure and
substructure within the Milky Way’s dark matter halo, the dark matter properties of one galaxy are
ultimately insufficient to effectively constrain the nature of dark matter. Hence, we need to examine
the dark matter within multiple galaxies. Fortunately, numerous current and upcoming observing
facilities will reveal thousands of streams around galaxies beyond the Milky Way, presenting the
opportunity to probe the dark matter halos they reside in with the technology we have developed for
the study of our own Galaxy and its stellar streams. In this thesis, we explore the insights on dark
matter that can be gained from observing extragalactic streams. We do so by testing our ability to
recover properties such as the dark matter halo’s mass and radial profile by generating and fitting
mock extragalactic streams and observations given the significant degradation of data expected
from observing stellar streams outside of the Milky Way. Additionally, given the emergence of
stellar streams within cosmological simulations of galaxy formation, we compare the properties of
stellar streams from the VINTERGATAN simulation suite to those of the Milky Way to determine
their authenticity. Finally, we then use the same simulation suite to create mock extragalactic stream
observations to inform the upcoming ARRAKIHS mission which will target external streams and
compare the results to current observations of streams around the Andromeda Galaxy. This thesis
concludes with implications and directions for future work based on our results.