Sofia Rojas Ruiz

UCLA

Physical Properties of Galaxies in the First 700 Million Years as Revealed by JWST

When: Wednesday 12 Nov 2025
12:00–1:00 pm PST
Where: Broida 3302
Series: A weekly informal gathering of UCSB, LCO and KITP astrophysicists to hear about current research by locals and visitors.

From the calendar

I will present the latest results on the physical characteristics of galaxies within the first 700 Myr (at redshift z>8), as studied with the BoRG-JWST survey. This unique spectroscopic campaign uses NIRSpec to follow up HST-selected galaxies at z ~ 8 across >300 independent sight lines, minimizing cosmic variance and providing a robust view of the bright galaxy population at this epoch. I constrain the UV luminosity function (UVLF) and stellar mass-to-light ratios, finding a higher bright-end UVLF than in legacy JWST fields, easing tensions with observations of galaxies at z > 10. The BoRG-JWST galaxies exhibit properties akin to the so-called “blue monsters” at z > 10 which are UV-bright, dust-poor, and massive, making them ideal analogs for studying early galaxy formation. I accomplish this by using the BoRG NIRSpec spectra to investigate their star formation histories, dust content, and potential AGN signatures. To address the challenge in disentangling star-forming galaxies from AGNs, I will discuss ongoing efforts using machine learning tools to classify these sources across all JWST NIRSpec surveys.

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