Abstract
Dwarf galaxies provide unique insights into the cosmology of our Universe. They are
at the scale most sensitive to the properties of dark matter and the physical processes
governing their evolution. They are, therefore, an ideal laboratory for testing dark matter
and galaxy formation models. Furthermore, due to new surveys like SDSS and DES, the
number of known dwarf galaxies in the Local Group and beyond continues to grow, with
upwards of 50 detected within the Milky Way to date. Due to their close proximity, we can
resolve these into their individual stars, providing stellar velocities, metallicities, and star
formation histories for hundreds to thousands of members. In this work I present a suite
of cosmological simulations designed to probe the low-mass dwarf regime in a Lambda
Cold Dark Matter (ΛCDM) cosmology at a mass and spatial resolution of 100 M sun and
3 pc respectively.
First, I present a selection of dwarf galaxies produced as part of the Engineering Dwarfs
at Galaxy formation’s Edge (EDGE) simulation suite and show they conform to all known
observations of dwarf galaxies to date.
Then, I investigate the cusp-core problem in the very smallest dwarf galaxies. I find
that even galaxies with M∗ ∼ 10^5 M sun can have their inner dark matter density lowered
by baryonic processes. This proceeds via two heating mechanisms, the typical ‘gas flow’
mechanism and a subdominant ‘minor merger’ mechanism. I also show that cusps can be
regrown as a result of dense mergers.
Next, I follow up with more detailed analyses to test whether my simulations can
explain the lone star cluster discovered in the ultra faint dwarf galaxy Eridanus II. This
includes the development of a large suite of star cluster simulations. I find that none of
the 1×10^9 < M200/M sun < 2×10^9 EDGE dwarf simulations run to date produce a core
substantial enough to explain the properties of the star cluster in Eridanus II. I discuss
possible explanations for this discrepancy and how these can be tested.
Finally, I explore whether the aforementioned dark matter heating has any measurable
impact on the halo shape in EDGE simulation. Above M200 ∼ 3×10^9 Msun , halo shapes
become more oblate and aligned with the angular momentum vector of the gas out to 5-10
times the stellar half light radius. This effect owes to gas dissipation rather than cusp-core
transformations. Below M200 ∼ 2×10^9 Msun , haloes retain their typically prolate shapes
as in pure dark matter ΛCDM simulations. I predict, therefore, that reionisation fossils
should be triaxial, providing a novel means to test cosmological models and the nature of
dark matter.