I use observation (especially high-resolution stellar spectroscopy) and astrostatistics to understand dwarf galaxies and metal-poor stars both as individual objects and as a population. I'm also interested in methods in stellar spectroscopy and scientific writing.
High-resolution spectroscopy
Ultra-faint dwarf galaxies (UFDs) represent the low-mass, low-metallicity extreme of galaxy formation and evolution. The chemical abundances of stars in UFDs reflect the conditions of star formation and metal production in the early universe, and their most metal-poor stars may preserve the fragile signatures of metal-free Population III supernovae. I'm involved in efforts to expand our small samples of information-rich high-resolution spectroscopy in these chemically-primitive systems, as well as to follow up other metal-poor stars in the halo, globular clusters, and stellar streams.
Statistical approaches to chemical enrichment
Galactic chemical evolution is a complex, multi-scale phenomenon--everything from nucleosynthesis to galaxy mergers affects a galaxy's chemical composition. We can use statistical samples of multi-element chemical abundances in more massive (but still relatively simple) classical dwarf spheroidal galaxies to constrain these baryonic processes. Thanks to decades of study, we have a relatively good phenomenological understanding of many aspects of galactic chemical evolution, but robust, quantitative constraints are challenging due to complex degeneracies, noisy and incomplete data, and the limitations of our theoretical models and simulations. To address these challenges, I am interested in developing methods for robust statistical inference and in uncertainty quantification.
Previous projects
Multi-galaxy constraints on chemical enrichment
Some of processes that govern chemical evolution, like nucleosynthesis, are the same in every galaxy. Others are completely environmentally dependent. I developed a statistical model of multiple galaxies to constrain these universal processes using a novel data-driven physical model called _dleiy_. I applied this model in a pilot study to the dwarf galaxies Sculptor and Fornax to constrain chemical enrichment in low-mass, metal-poor environments. We found a large fraction of prompt Type Ia and an enhanced rate of Type Ia supernovae, which may suggest a metallicity dependence of Type Ia enrichment.
High-resolution spectroscopy of UFDs Eridanus IV and Centaurus I
I conducted the first high-resolution follow-up of the UFDs Eridanus IV and Centaurus I to measure the chemical abundances of their brightest star. The star in Eridanus IV is a carbon-enhanced metal-poor star with no neutron-capture enrichment, suggesting its carbon enhancement is intrinsic (reflective of its birth cloud). The origin of carbon enhancement and its role in star formation in the early universe are still not fully understood, but carbon-enhanced metal-poor stars are considered candidates for true second generation stars. However, the chemical composition of the star in Eridanus IV suggests that Pop III enrichment alone is unlikely. This work was done as part of the DELVE collaboration.
Spectroscopic confirmation of two new UFDs
Small-scale structure is dictated by the microphysical properties of dark matter, so a complete, well-characterized census of lowest-mass dwarf galaxies provides strong tests of the dark matter paradigm. As part of the DELVE collaboration, I conducted the first follow-up of two (at the time) recently discovered stellar systems, Eridanus IV and Centaurus I. This work confirmed that both are in fact dwarf galaxies, rather than star clusters. We found that Eridanus IV has an unusual, right-skewed metallicity distribution and a low mean metallicity. Its characteristics provide indirect evidence that the observed plateau in the ultra-faint regime in the otherwise tight magnitude-metallicity relation may be driven by feedback/pre-enrichment.