Tom Rose & Congyao Zhang

Talk 1: Tom Rose, 3:00pm - 3:30pm
Observing AGN fueling via molecular absorption lines
Molecular gas plays a significant role in powering AGN. Unfortunately, observing this gas on small spatial scales is difficult because it can normally only be seen en masse through emission lines. I will present observations of molecular gas in several massive galaxies on scales of just a few hundreds of solar masses. To do this we use the galaxies’ bright continuum sources — against which we see the shadows of gas clouds in the form of absorption lines. I will explain how some of these observations show the early stages of AGN accretion. The absorption lines can also be used to infer the clouds’ mass, temperature, and chemistry. Through this, we show that the gas clouds fuelling AGN have remarkably similar properties to gas in the Milky Way.

Bio: Since completing my PhD at Durham University in 2021, I have been postdoctoral fellow at the University of Waterloo. My research focuses on radio observations of molecular gas in the most massive galaxies, with a particular focus on ALMA. I am also interested in how the molecular gas of these galaxies is related to their X-ray properties, which I now plan to investigate with XRISM.

Talk 2: Congyao Zhang, 3:30pm - 4:00pm
Buoyant bubbles in galaxy clusters and their role in shaping cluster cores
Bubbles of relativistic plasma are essential for AGN feedback in galaxy clusters, stirring and heating the intracluster medium (ICM). In observations, bubbles are often found maintaining their integrity and sharp edges during their buoyant rise, much longer than hydrodynamic predictions. In this talk, I will show our novel model designed to capture the long-term interaction between intact bubbles and their ambient ICM, and demonstrate that such interactions play an important role in generating g-waves and shaping multiphase gas in cluster cores. In our model, large eddies are formed in rising bubble’s wake, responsible for most of the gas mass uplift from the cluster center. These eddies are elongated by the strong stratification of the ICM and eventually detached from the bubble surface. This picture naturally explains the presence of long straight and horseshoe-shaped Hα filaments in the Perseus cluster, inward and outward motions of the gas, and the X-ray-weighted gas velocity distributions near the northwestern bubble observed by Hitomi, and will help shed light on how we interpret future observations from, e.g., XRISM, Athena.

Bio: Congyao Zhang is currently a postdoctoral scholar at the University of Chicago. He received his PhD degree at the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University in 2016 and then worked at the Max Planck Institute for Astrophysics (MPA) as a postdoctoral researcher from 2016 to 2019. His research interests are galaxy clusters, large-scale structures, and cosmology. Collaborating closely with both theorists and observers, he has been applying analytical and numerical modeling to understand (1) formation and evolution of galaxy clusters and (2) how to use these massive structures to investigate plasma physics and cosmology.