A Multiwavelength Study of the Physics of the Intracluster Medium, Its Multiple Phases and AGN Feedback

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Clusters of galaxies are the largest gravitationally bound structures in the Universe. Baryonic matter, unlike the dominant dark matter, is accessible to direct observations. It is found within individual galaxies as stars and as a hot tenuous gas, dubbed the ICM, filling the space between galaxies. As the ICM cools it radiates in the x-ray part of the spectrum. Left unattended it will continue to cool, radiating in the ultraviolet, optical, and infrared. Ultimately the gas should cool to tens of degrees and be bound in giant molecular gas clouds that collapse to form stars. At the center of a rich cluster sits a massive bright elliptical galaxy, the Brightest Cluster Galaxy (BCG), which houses a super-massive Black Hole (SMBH) at its nucleus. It is believed that the SMBH re-supplies energy to the ICM as some of the cold gas that condenses from the ICM falls onto an accretion disk around the Black Hole, ultimately adding to the mass of the Black Hole and fuelling the ejection of a powerful outflow. This outflow carries energy, magnetic fields, and relativistic electrons into the ICM where it can re-supply energy lost through radiation. Recent observations with radio and X-ray telescopes have provided new high quality images showing the outflow excavating cavities and driving pressure waves into the ICM. Thus it is clear a complex interplay exists between cooling and heating, inflow and outflow, accretion and growth. The same physical processes operating in clusters today likely occurred during galaxy formation 5-10 billion years ago. Astronomers believe that the growth of the galaxy and its central black hole are coupled via feedback process. The feedback between the medium, galaxy growth, and the central black hole must operate over billions of years, and on size scales from parsecs to hundred of thousands of parsecs. Thus, the ICM is a dynamic place where heating and cooling processes vie for dominance, super-massive black holes grow at the centers of galaxies, and an uneasy equilibrium is maintained. The major objective of this work is to uncover how feedback mechanisms operate in the centers of clusters by developing a detailed understanding of the physical processes at work. With my NSERC Discovery grant, I will conduct a multi-wavelength observational study of nearby clusters, to map the spatial, thermal, and temporal evolution of the baryonic matter, determine the system energetics, and identify the dominant feedback loops at play. Working with 4 HQP from high school through postdoc, we will have assembled a detailed picture of the spatial distribution, kinematics, mass content, and energetics of each phase of the baryonic matter in these complex systems. Impact: this work will create the information that we and other astronomers use to develop our understanding of the feedback mechanisms and macro-evolutionary laws that govern cluster and galaxy evolution.