DEPARTMENT OF PHYSICS DISSERTATION DEFENSE: Bernardita Ried Guachalla

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Title: 

Tracing Cosmic Baryons with the Sunyaev-Zel'dovich Effects

Abstract: 

The cosmic microwave background (CMB) constitutes one of the most powerful probes of the expanding Universe. Originating approximately 380,000 years after the Big Bang, this relic blackbody radiation is remarkably isotropic, with small temperature fluctuations, known as primordial anisotropies, that encode fundamental information about the physics and composition of the early Universe. Beyond its primary anisotropies from the early Universe, the CMB also carries imprints of the late-time Universe: as CMB photons traverse the evolving cosmic web, they acquire secondary anisotropies through interactions with intervening structures formed during cosmic evolution. In particular, inverse Compton scattering of CMB photons off energetic electrons in ionized gas gives rise to the Sunyaev–Zel'dovich (SZ) effects. The thermal component (tSZ) traces the integrated pressure of hot gas, while the kinematic component (kSZ), arising from Doppler shifts due to bulk motions of electrons, probes the momentum field of baryons. These effects provide complementary observables, enabling the CMB to act as a cosmic backlight for studying ionized gas across a wide range of halo masses and redshifts. Such measurements offer a unique avenue to address outstanding problems in astrophysics and cosmology, including: the distribution of the ``missing baryons'' in circumgalactic media; the efficiency and spatial extent of feedback processes in galaxy formation; and the characterization of baryonic physics for precision weak gravitational lensing analyses. Recent advances in survey capabilities are enabling increasingly precise measurements of these signals across cosmic time. The combination of data from the Atacama Cosmology Telescope (ACT) with