Galaxies and Cosmology Seminar

Natalia Villanueva, The University of Texas at Austin

High-Redshift Galaxies at Pixel Scales: Spatially-resolved methods for selecting early galaxies and constraining their star-forming nature

JWST’s exceptional depth and wavelength capabilities has pushed our frontier for finding high-redshift galaxies, and its high spatial resolution allows us to tie observed galaxy properties to their morphological structure better than ever before. However, robust selection of high-redshift galaxy candidates from photometry is challenged by contaminating look-alike sources, and morphological analysis of early galaxies is challenged by limits of morphology-fitting tools. We present works addressing both areas: (1) We apply machine-learning to improve the efficiency and robustness with which high-redshift galaxy candidates can be identified against contaminants in photometry with the tool SEDFlow, where we infer galaxy properties pixel-by-pixel to decompose high-redshift galaxies from overlapping low-redshift counterparts. (2) We measure the rest-UV, -optical, and -Halpha sizes of z~4-5 galaxies with the morphology-fitting tool Forcepho to spatially resolve their star formation growth. We find that for the most actively star-forming galaxies, Halpha sizes are ~2-3 times larger than rest-UV sizes, and up to ~10 times larger than rest-optical sizes, constraining the physical processes driving extremely short timescales of star formation and feedback in early galaxies.

Kaelee Parker, The University of Texas at Austin

Cutting through the Clouds -- Comparing Indirect Tracers of Ionizing Photon Escape

The Epoch of Reionization provides fundamental insights into the properties of early galaxies and their role in shaping the universe as we observe it today. For the 45 nearby star-forming galaxies in CLASSY, I have estimated the fraction of escaping ionizing radiation using five indirect but independent approaches. The combination of these UV diagnostics allow us to more robustly constrain the escape fraction for this sample, explore any systematic differences between these methods, and investigate how properties of the host galaxy and their stellar populations can influence the amount of ionizing radiation that escapes into the intergalactic medium. The high-S/N and high-resolution of their FUV spectra allow for detailed study of how these properties are related, which can be used to predict the neutral gas properties and ionizing photon escape of galaxies at higher redshifts.