Star Formation Histories of UV-Luminous Galaxies at z~7
A key component of understanding galaxy formation and evolution in the early Universe, and how these objects drove the process of cosmic reionization, is understanding the cosmic star formation history. It is currently unclear whether the population of UV-luminous, star-forming galaxies decreases precipitously at very early cosmic times (z > 9), or if the decline is more gentle.
In Whitler et al. (2022), we quantified the distribution of ages and star formation histories of UV-bright galaxies at z~7, and examined the implications of these ages for the UV-luminous galaxy population at z~9. We found that ~30% of the bright z~7 population could be sufficiently mature to exist at z~9, though the exact proportion depends strongly on the physical model assumed when inferring the physical properties of individual galaxies.
Inferring the Reionization Timeline from Lyα
Lyα is highly susceptible to attenuation by neutral hydrogen, so can be used to infer information about the quantity and distribution of neutral hydrogen in the IGM during the EoR. I worked with Charlotte Mason at the Center for Astrophysics | Harvard & Smithsonian to improve a physical model of Lyα transmission through the intergalactic medium, to be used to infer the timeline of cosmic reionization from observations of Lyα emission from galaxies. Specifically, I implemented scatter in the relation between galaxy UV luminosity and dark matter halo mass and inferred the volumetric neutral fraction at z~7 with the improved model.
See the paper here.
The Hydrogen Epoch of Reionization Array
Another method of studying reionization comes directly from the neutral hydrogen in the IGM. Neutral hydrogen emits radiation with a wavelength of 21 centimeters during its spin-flip transition, and this spectral line is a promising probe of the EoR. However, actually detecting the line requires overcoming significant observational challenges. These effects can be environmental (e.g. bright radio foregrounds from galactic and extragalactic sources, radio frequency interference, and atmospheric attenuation), or instrumental (e.g. calibration errors).
The Hydrogen Epoch of Reionization Array (HERA) is a radio interferometer currently under construction in South Africa designed to probe the large-scale structure during reionization via power spectral measurements of 21 cm line. I used HERA commissioning data to examine the effects of radio frequency interference and calibration systematics on measurements of the 21 cm power spectrum from the EoR, with the eventual goal of understanding the impacts of these systematics on astrophysical parameter estimation from 21 cm EoR measurements.
The Radio Halo of NGC 4565
I imaged the nearby edge-on galaxy NGC 4565 with data from the Low Frequency Array (LOFAR) at 144 MHz from the LOFAR Two-meter Sky Survey. Using this low frequency image, I created vertical intensity and spectral index profiles and characterized the cosmic ray transport mechanism in the galaxy as being primarily diffusive, rather than advective. This has implications for galactic outflows and the transfer of energy and heavy elements between the interstellar, circumgalactic, and intergalactic media.
See the paper here.
Modelling Far-Infrared Line Emission from Galaxies
I contributed code to the SImulator of GAlaxy Millimetre/submillimetre Emission (SÍGAME) module, a code to post-process the results of cosmological galaxy formation simulations to extract the far-infrared line emission of galaxies. I primarily added analysis capabilities, including calculating radial profiles of a given far-infrared line and maps of line emission ratios (e.g., [CII]158μm/[NII]205μm). I also worked towards validation efforts, compiling observations of far-infrared lines at both high and low redshift to compare to simulation results.