My research focuses on galactic chemical evolution: how galaxies form stars, cycle gas, and build up the chemical elements across cosmic time. I combine ALMA and JWST observations with chemical evolution models to connect molecular lines and elemental abundances with star formation histories, stellar yields, gas inflow and outflow, and possible variations in the stellar initial mass function.
CO Isotopologues as IMF Tracers#
The stellar initial mass function (IMF) is fundamental to how we infer star formation rates, stellar masses, feedback, and galaxy evolution. In my PhD work, I use the 13CO/C18O isotopologue ratio as a tracer of IMF variations in high-redshift galaxies. The physical motivation is that most 13C is produced by low- and intermediate-mass stars, while much of 18O is produced by massive stars. Their abundance ratio therefore carries information about the stellar populations that enriched a galaxy.
With sensitive ALMA observations and careful data reduction, I recovered weak CO isotopologue emission in strongly lensed galaxies at cosmic noon. In a high-redshift main-sequence galaxy, I detected 13CO and C18O and measured a low isotopologue flux ratio, providing evidence for a more top-heavy IMF than in local main-sequence systems. This result was published in The Astrophysical Journal in 2024.
I am extending this work to a larger sample of high-redshift starburst galaxies using new ALMA observations and archival ALMA/VLA data. The goal is to test whether low 13CO/C18O ratios are common in intense star-forming environments and to connect these ratios with the evolutionary stage of starbursts.
Galactic Chemical Evolution Models#
Chemical abundances are shaped by many processes at once: the IMF, stellar yields, star formation histories, gas accretion, outflows, stellar mass growth, and galaxy assembly. I use galactic chemical evolution (GCE) models to turn these coupled processes into testable predictions for observed abundance patterns.
During my PhD, I worked extensively with the open-source GCE code NuPyCEE and developed model frameworks that combine traditional chemical evolution assumptions with more realistic star formation histories from semi-analytical galaxy formation models. One project tests whether sodium can trace high-mass IMF variations in main-sequence galaxies. The result, accepted by Astronomy & Astrophysics, shows that sodium abundances in these systems have only a limited imprint of high-mass IMF variations, while also establishing a flexible framework for testing other elements.
Stellar Yields and Chemical Fingerprints#
I am interested in improving the physical realism of GCE models through more complete stellar yield prescriptions. This includes massive stars, AGB stars, very massive stars, low-metallicity populations, and binary evolution. Because binary interactions are common but often simplified in galaxy-scale chemical evolution studies, incorporating their yields is an important next step for interpreting abundance patterns in the early Universe.
These models can help identify which elements or isotopes are most sensitive to the IMF, which trace star formation histories, and which preserve information about extreme stellar populations.
JWST, Cosmic Dawn, and Early Enrichment#
JWST has opened a new window on galaxies in the early Universe, revealing strong carbon and nitrogen enrichment, high circumgalactic metallicities, very blue UV spectra, and luminous nebular emission in young systems. I aim to test whether these observations can be explained by top-heavy IMFs, extremely metal-poor stars, and enrichment channels such as hypernovae, pair-instability supernovae, and rapidly rotating stars.
By combining JWST abundance measurements with ALMA molecular-line constraints and GCE modeling, I hope to build a coherent picture of how the first generations of galaxies enriched their gas and formed stars.
Starburst Timescales#
My future work also uses 13CO/C18O together with star formation rates as a potential clock for starburst evolution. GCE models predict that the isotopologue ratio changes rapidly during the early stages of a burst before settling to a lower equilibrium value. Comparing these predictions with nearby systems and high-redshift starbursts can help constrain when intense star formation was triggered and how quickly it reshapes a galaxy’s chemical state.