RSAA Colloquium: Glenn Kacprzak (Swinburne)

Beyond the Galaxy: Tracing the Baryon Cycle through the Circumgalactic Medium

To understand how galaxies evolve, we must look beyond their stellar disks. Galaxies are embedded within vast reservoirs of diffuse gas known as the circumgalactic medium, which contain the fuel for future star formation, material expelled by feedback, and a record of the interactions between galaxies and their environments. Yet this gas is faint, multiphase and difficult to observe. 

In this talk, I will show how background quasars and gravitationally lensed galaxies can be used as cosmic flashlights to map the gas surrounding galaxies. By combining absorption line spectroscopy with galaxy imaging, kinematics, chemical abundances and spatially resolved emission, we can connect the location, motion and metallicity of halo gas to galaxy orientation, rotation and star formation. I will present evidence for gas accretion, recycling and outflows, while highlighting the challenges involved in distinguishing these processes observationally. I will also discuss new approaches that move beyond individual quasar sightlines, using gravitational arcs and integral field spectroscopy to build tomographic maps of the circumgalactic medium. Together, these observations are transforming the circumgalactic medium from an unseen reservoir into a measurable ecosystem, and clarifying how galaxies acquire gas, regulate their star formation and ultimately shut down.