My group works on a wide range of projects in observational cosmology and galaxy evolution. Here I have listed a few brief descriptions of some of the main research avenues that we are currently exploring.

Using Strong Lensing to Magnify the Distant Universe

Magnified studies of distant galaxies are becoming a powerful way to understand the astrophysical processes that are responsible for understanding how the stars and galaxies that we observe in the Universe were formed. In the distant universe we have, historically, studied star and galaxy formation galaxy-by-galaxy, because most of our observational facilities can only marginally resolve structures smaller than the typical size of a galaxy (~1000 parsecs). However, the fundamental unit of star formation in the universe is not a star, nor a galaxy, but rather a star forming region with a typical scale of order ~10s to 100’s of parsecs. We can only resolve the relevant physical scales in distant galaxies that are magnified by natural telescopes. A major focus of my research group at UC is use strong lensing systems to study the signatures of star-formation on the relevant physical scales and constrain the astrophysical processes that explain how galaxies have formed their stars across cosmic time. We use observations from the best ground- and space-based telescopes available (including the James Webb Space Telescope, the Hubble Space Telescope, the Chandra X-ray Observatory, and JWST) to measure the internal properties of star-forming galaxies, as described in more detail below and in my accompanying teaching statement.

Example papers: Wuyts+2012, Bayliss+2014b, Rigby+2015, Bayliss+2017, Johnson+2017, Rigby+2018, Rivera-Thorsen+2019, Bayliss+2020, Kim+2023b

Currently working on this: Josh Roberson, Riley Owens

Some particularly exciting results:

From Bayliss et al. (2020). We measured spatially resolved emission from high mass X-ray binaries (HMBXs) at Cosmic Noon, opening up a new window into high energy studies of resolved, distant star-forming regions.

From Rivera-Thorsen et al. (2019), Kim et al. (2023b), and Owens et al. (2024, submitted). We have been centrally involved in the discovery and characterization of the Sunburst Arc, a strongly lensed LyC leaking galaxy that is a unique laboratory for exploring the physical scale and conditions associated with the highly anisotropic escape of ionizing radiation from a typical UV-bright star-forming galaxy.

Strong Lensing Galaxy Clusters As Cosmological Laboratories

The broadest goal of observational cosmology is to understand the structure, composition, and physical laws that make up the observable universe. A major challenge is measuring how the main constituents of the universe – normal/baryonic matter, dark matter, and dark energy – form large, gravitationally bound structures, the largest of which are galaxy clusters. Measuring the properties of galaxy clusters is an effective way to test cosmological theories of structure formation, but we are limited in our ability to directly measure quantities like mass, which typically have to be inferred from observations of electromagnetic radiation. Gravitational lensing provides a work-around, however, because the lensing effect directly constraints the amount of matter in a gravitational lens, as well as how that matter is distributed. We use systems with well-constrained gravitational lensing constrains to measure their total lensing masses, and combine that information with other measurements of the total baryonic and stellar mass components. Ongoing work by students in my group uses large ground-based telescopes along with Hubble and Chandra to measure the mass distributions within massive galaxy clusters that act as strong lenses and compare those measurements to predictions from leading cosmological models of structure formation. 

Example papers: Bayliss+2011a, Bayliss2012, Oguri+2012, Bayliss+2014a, Bayliss+2015, Sharon+2020

Currently working on this: Raven Gassis, Lauren Elicker, Prasanna Adhikari

JWST ERS Data Reduction: Testing and Documenting Pipelines

As part of the JWST TEMPLATES ERS program, members of my group are working to test and document the JWST data pipelines, which are still in their very early days. We are also engaged in the wave of exciting new science coming out of the TEMPLATES JWST data. The summer 2023 work with NIRSpec resulted in post on Astrobites!

Currently working on this: Lyn Wang, Paul Smith, Eli Meisel, Emmy Bursk, Joshua Tiju, Kristen Tucker

Galaxy Evolution and Cosmological Constrains From Galaxy Cluster Surveys

I am a Senior Member of the South Pole Telescope (SPT) cluster collaboration spanning the SPT-SZ, SPT-Pol, and SPT-3G surveys. My group is involved in multi-wavelength follow-up of the Sunyaev Zel'dovich selected cluster samples that are detected in the SPT-3G survey data. Results from this work include cluster sample characterization, cosmological parameter constraints, and measurements of environmental quenching in the cluster galaxy population.

Some relevant papers: Bleem+2015, Bocquet+2019, Zohren+2022, Kim+2023a, Bocquet+2024

Currently working on this: Raven Gassis, Prasanna Adhikari, Nathan Hoffmann, James Leighton

SPT-GMOS Spectroscopic Survey of Cluster Galaxies in the SPT-SZ 2500 squ. deg survey.

As a postdoc I lead an NOAO survey program providing the large majority of the spectroscopic follow-up of SPT-detected galaxy clusters. These observations provided critical information to calibrate the redshift estimates for the sample, provided complementary cluster mass estimates via velocity dispersions, and have fed several analyses of the properties of the cluster galaxy population, including star formation histories of passive galaxies and environmental quenching. 

Some relevant papers: Bayliss+2016, Bayliss+2017a, Khullar+2022