While the vast majority of the light from our galaxy comes from the Galactic disk, the vast majority of the mass of the MW is in its dark matter (DM) halo. Because we cannot directly observe the MW's DM halo, we must use luminous tracer populations to study the mass distribution indirectly. Fortunately, there are stars strewn throughout the MW's DM halo. According to the hierarchical paradigm for galaxy evolution, the MW built up its halo of dark matter over cosmic time by accreting smaller dwarf galaxies. The remnants of these accreted dwarfs make up the MW's stellar halo. Halo stars can therefore be used both to constrain the dark matter distribution of the MW as well as inform us about the galaxies in which they formed.
Specifically, my research interests have two main branches: 1) mapping the dark matter distribution and disequilibrium in the MW and 2) using halo stars to study the faint, low-mass galaxies that were consumed by the MW during its formation.
During my PhD thesis, I led the Halo Assembly in Lambda-CDM: Observations in 7 Dimensions (HALO7D) survey (Cunningham et al. 2016, 2019a, 2019b). HALO7D consists of Keck spectroscopy and proper motions measured from the Hubble Space Telescope imaging. I led the observations, kinematic measurements and analysis for HALO7D.
Synthetic color image of the galaxy m12i, from the Latte suite of FIRE-2 cosmological simulations. The galactic disk is embedded in a DM halo. Stars from tidally disrupted dwarfs are strewn throughout the DM halo: this is the stellar halo. Image credit: Phil Hopkins.
My recent work as a Flatiron Research Fellow at the CCA has involved developing new analysis methods within simulations (both cosmological hydrodynamical simulations as well as N-body simulations). In Cunningham et al. (2020), I developed a quantitative description of the kinematic structure of the halo in order to quantify disequilibrium on different spatial scales, utilizing spherical harmonic expansion. In Cunningham et al. 2021, I explored a method for leveraging the observed MW halo chemical abundance ratio distribution (CARD) to infer the properties of the dwarf galaxy progenitors of the stellar halo.