Probing AGN-Inflated Cavities in Galaxy Cluster MS 0735+74 with the Sunyaev-Zel'dovich Effect

We report the first detection of the Sunyaev-Zel'dovich (SZ) signature of cavities in the intracluster medium (ICM) associated with radio-mechanical feedback from an active galactic nucleus (AGN) in the center of a galaxy cluster. Such cavities are seen as regions of reduced brightness in X-ray images; while this reduction in brightness requires a significant local reduction in ICM density, X-ray data alone cannot easily constrain the temperature or nature of the material within the cavities. However, measurements of the SZ effect from these structures can begin to shed light on their contents, when combined with X-ray constraints on the pressure of the surrounding gas. We have mapped galaxy cluster MS 0735+74, which hosts the most powerful AGN outburst known, at 30 GHz using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). We find a clear reduction of the SZ signal in the direction of the cavities within the cluster, corresponding to a deficit of ambient-temperature plasma, as indicated by the X-ray data. Thermal support of the cavities by gas with a temperature of less than several hundred keV can be ruled out, while cosmic rays or magnetic fields providing non-thermal support are still viable options.