Research
I am an extragalactic astronomer who uses spectroscopy to study galaxies across cosmic time. My work revolves around use of large surveys from primarily space-based observatories like the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST). I have had the great privilege of being a part of some wonderful collaborations, including CEERS (pictured above), NGDEEP, and RUBIES. Here you will find some selected results from my recent work. You can also access my code on GitHub.
For those interested in working with me or in my field, I have written a brief guide about getting started with research.
High-Ionization Emission Lines
The early universe in the Epoch of Reionization (z>6) was likely reionized by energetic photons from low-mass, metal-poor galaxies. We often study galaxies like these using their spectra to look for emission lines which require large amounts of energy to create. The 'high' ionization regime of emission line spectroscopy is often defined using emission lines of higher creation potential than singly ionized oxygen (13.62 eV), and the 'very high' ionization regime defined as higher creation potential than doubly ionized oxygen (35.12 eV). I study extremely high-ionization galaxies which emit photons from quadruply ionized neon (97.11 eV) in the near-ultraviolet ([Ne V] λλ3346,3426). The obvious question is: What creates radiation energetic enough to produce [Ne V]?
There are at least three plausible sources of radiation to create [Ne V] and other extremely high ionization emission features. Active galactic nuclei (AGN) are the most obvious source, but several objects in our sample and in the literature are not consistent with classification as AGN. The sparse literature to this point disagrees on the cause: some works claim it must be AGN all the time; others argue that supernova shocks or Wolf-Rayet stars are most likely.
My work has shown that, at least at z~2, [Ne V] very strongly traces accreting supermassive black holes. However, my next work shows that this may not hold at all redshifts. The early results from JWST have shown that there may be many previously unknown AGN in the early Universe, so new and robust selection methods for this epoch are critical.
I utilize photoionization modeling in conjunction with observations in an effort to develop AGN selections that are robust to many different epochs of cosmic time. I find that [Ne V] may be produced by traditional AGN, but also by accreting intermediate mass black holes and elusive Population III stars. While the field of discriminating between ionizing sources at early times is very much in its infancy, there is some promise that high-ionization lines may offer necessary insight.
Near-Infrared Emission-Line Star Formation Rates and Dust Attenuation
Extragalactic star formation is often inferred from UV and optical tracers such as UV continuum luminosities and H-alpha or other emission line fluxes. These are great measures of recent star formation, except in the presence of dust in the interstellar medium. We study star formation rates derived from the near-infrared Paschen lines of hydrogen, which directly trace near-instantaneous (<10 Myr) SFRs with the same benefits of the Balmer lines' insensitivities to metallicity, temperature, and density. Notably, Paschen lines have the added benefit of being much less sensitive to interstellar dust attenuation.
We also study the implications of Paschen to Balmer line flux ratios, like Pa-beta/H-alpha, which can be used as a measure of the interstellar dust attenuation in a galaxy. This is much like the classic Balmer decrement (H-alpha/H-beta), but can be used for much dustier galaxies since the Balmer lines become too heavily attenuated for accurate measurements.