How Feedback Shapes Galaxies and the Stories We Tell About Science

Abstract

Galaxies evolve through a continuous exchange of mass and energy with their surroundings, a process known as the baryon cycle. ``Feedback" from stars and supermassive black holes, in the form of radiation and winds, is predicted to regulate this cycle by modulating how gas cools, forms stars, and is reheated and/or expelled. This dissertation explores how feedback operates across a range of environments and mass scales, using a combination of multi-wavelength observations and theoretical modeling. The first two chapters examine the impact of supermassive black hole / active galactic nuclei (AGN) feedback in the Universe's most massive galaxies through multi-wavelength observational studies of the SDSS J1531+3414 ($z = 0.335$) and Abell 2597 ($z = 0.0821$) clusters of galaxies. In SDSS J1531+3414, I identify one of the most powerful AGN outbursts known, releasing over $10^{61} \mathrm{~erg}$ of energy. This outburst is traced by a giant X-ray cavity and steep-spectrum fossil radio lobes, with a reservoir of $\sim 10^{10} \mathrm{~M_\odot}$ of molecular gas tangentially connected to it. The gas appears to have been uplifted by the powerful outburst, and is now spatially offset from a striking 28 kpc-long chain of 19 stellar superclusters. Together, these features suggest that a recent major merger has disrupted the feedback loop in the cluster's central massive galaxy, decoupling star formation from the cold gas that fuels it. In contrast, Abell 2597 hosts a more stable, long-lived feedback loop. Deep \textit{Chandra} X-ray observations reveal multiple generations of AGN feedback-driven cavities and potential 150 kpc-scale shocks, consistent with recurrent AGN outbursts on $\sim$10$^7$ year timescales. Although the AGN injects mechanical energy at a rate of $\sim 10^{44}$ erg s$^{-1}$, sufficient to prevent overcooling, infrared and millimeter observations reveal that residual cooling persists at $\sim$15 \msun\ yr$^{-1}$, maintaining a $\sim10^9$ \msun\ cold gas reservoir draped around the cavities in the central galaxy. These features point to ongoing condensation from the intracluster medium, likely aided by AGN-driven uplift, and suggest that cold gas accretion—not hot-mode Bondi flow—sustains the central AGN. To extend this analysis beyond the massive galaxies at the centers of clusters and into the lower-mass regime where stellar feedback dominates, Chapter 3 introduces the TNG SAM, a new semi-analytic model of galaxy formation. Built on the Santa Cruz SAM framework and calibrated to baryon flows measured in the IllustrisTNG-100 simulation, the TNG SAM captures key physical processes shaping galaxies in halos from $10^{10}$ to $10^{12}\ M_\odot$. Several major updates distinguish the model: a cooling time-based prescription for gas accretion that replaces the classic hot/cold mode dichotomy; revised treatments of halo gas re-accretion and cooling; explicit modeling of both galaxy- and halo-scale outflows; and metallicity-dependent mass loading and metal enrichment prescriptions that track the circulation of gas and metals between galaxies and their environments. These changes allow the TNG SAM to reproduce IllustrisTNG predictions for stellar mass, cold and hot gas mass fractions, and gas and stellar metallicities to within $\sim 30%$, out to $z \sim 6$. As a result, the model offers a powerful, computationally efficient tool for interpreting the baryon cycle in galaxies where direct observations of the CGM remain limited. Finally, this dissertation turns from the physical processes shaping feedback to the infrastructures, labor systems, and politics that shape the production of astronomical knowledge. Drawing on archival and historical records, I examine the role of Black South African workers in building and maintaining early 20th-century American observatories in South Africa. These workers, whose contributions have been largely excluded from the scientific narrative, laid the physical foundations that enabled U.S. institutions to extend their scientific reach into the Southern Hemisphere. By recovering these histories, I trace how systems of racial capitalism and settler colonialism materially structured the development of modern astrophysics—not only through the land and labor they extracted, but also through the epistemologies they reinforced. Just as feedback governs the cycling of matter and energy in galaxies, it offers a lens for understanding how knowledge itself is generated, sustained, and challenged within scientific institutions.