Research
Understanding the origins of FRBs through their host galaxies and using FRBs as probes of foreground baryons.
Fast radio bursts (FRBs) are millisecond-duration radio flashes from distant galaxies. As each burst crosses the universe, free electrons along its path delay the lower frequencies, an effect measured by the dispersion measure (DM). My research follows two connected threads: understanding the galaxies and local environments that host FRBs, and using the bursts to measure the diffuse ionized gas between galaxies.
FRB host galaxies
What produces an FRB is still an open question, and where the bursts occur is one of the best clues. I use optical and infrared imaging and integral-field spectroscopy (with Keck/KCWI, Magellan/LLAMAS, HST, and other facilities) to resolve the star formation, gas metallicity, and ionization around precisely localized FRBs. Examples include the spiral-arm environment of FRB 190608, spatially resolved metallicity maps of five nearby hosts, and FRB 20250316A, localized to 13 pc. These measurements also determine how much of a burst’s dispersion arises in its own host galaxy, which must be subtracted before the burst can serve as a clean probe of the gas outside it.
As a member of the $F^4$ team, I participate in the planning, execution, and data reduction of optical observations of localized FRBs with telescopes such as Keck, Gemini, and SOAR.
FRBs as probes of cosmic baryons
Much of the universe’s ordinary matter is diffuse gas in the circumgalactic and intergalactic media (CGM and IGM), too faint to see directly. An FRB’s dispersion measure counts every free electron along its path, so once the Milky Way and the host are accounted for, what remains traces this gas.
I am involved in the FLIMFLAM survey, which maps the foreground galaxies along FRB sightlines to constrain how baryons are distributed between the CGM and IGM. Its first data release, covering eight sightlines, produced the first measurement of that split. I lead spectroscopic observational efforts with the Keck and Gemini telescopes for redshift estimation and am involved in imaging, spectroscopy, data reduction, and Bayesian inference for matter density reconstruction. I have also modeled how individual foreground galaxy halos and cosmic web filaments contribute to the DM of particular bursts, such as FRB 180924 and FRB 190608.
