MIfa Colloquium: Marc Rafelski (STScI)
Title: The Baryon Cycle in Action: Gas Recycling and Metallicity Trends in the ISM and CGM of Galaxies
Abstract: The formation and evolution of galaxies is governed by the baryon cycle — an intricate interplay of gas inflows, outflows, star formation, feedback, and recycling. Understanding this cycle requires tracing the evolution of metallicity and gas content in both the interstellar medium (ISM) and the circumgalactic medium (CGM). In this talk, I will present results from the MUSE Ultra Deep Field (MUDF), which enable us to probe the metallicity evolution and mass dependence of low-mass (M~10^7Msun), low star-formation rate (SFR~0.1Msun/yr) galaxies out to redshift z~2. The MUDF also includes two bright quasars at z~3.2, separated by ~500 kpc, whose sightlines intersect the IGM and CGM of these galaxies. This configuration allows us to directly connect galaxy properties observed in emission with gas seen in absorption. We find compelling evidence for gas recycling in the CGM of galaxies with high specific star-formation rates. I will also present new results from the KCWI Analysis of Gas around Galaxies (KAGG) survey, which significantly expands the sample of galaxies associated with absorption systems. In particular, we focus on Damped Lyman-alpha systems (DLAs), which trace large reservoirs of neutral hydrogen and provide robust metallicity diagnostics. Our findings show that these galaxies are detected at large impact parameters, suggesting extended distributions of neutral gas and confirming that high-redshift DLAs are integral components of the CGM. Finally, using the Qz5 survey of z~5 quasars, we examine the metallicity evolution of DLAs and the CGM. We confirm a steepening in metallicity decline beyond z > 4.7 and report, for the first time, that the cosmic HI mass density peaks at z~3–4. As expected, this is earlier in time than the peak in the star-formation rate density and molecular hydrogen mass density. These results provide critical constraints for future simulations of galaxy formation and the baryon cycle across cosmic time.
