Observational Cosmology Seminar

The redistribution of baryonic matter across cosmic structures connects the physics of galaxy formation to precision cosmology. Baryonic feedback can move gas from the inner regions of haloes into their outskirts and the surrounding cosmic web, altering both the observable gas distribution and the underlying matter distribution relevant for cosmological measurements. The thermal and kinematic Sunyaev–Zel'dovich (SZ) effects provide powerful probes of this diffuse ionized gas through its pressure and density.
In this talk, I will discuss my work using SZ observations and large-scale structure surveys to measure and interpret the baryon distribution. I will present measurements of the thermal SZ effect with DESI and ACT, but I will focus particularly on a new model-independent measurement of the radial gas fraction around DESI galaxies, obtained by combining kSZ measurements with galaxy-galaxy weak lensing. By directly combining the kSZ and lensing measurements, we measure substantial gas depletion in the inner regions of haloes and its recovery toward larger scales without assuming a gas profile or halo-mass calibration. I will then compare these measurements with hydrodynamical simulations and discuss how feedback, stars, neutral gas, and diffuse gas beyond halo boundaries shape the observed SZ signal. Together, these results provide a direct test of baryonic feedback models and help connect observations of circumgalactic gas to its impact on cosmology.