Intense AGN activity in the merging cluster Cygnus A

We report on a detailed spatial and spectral analysis of the large-scale X-ray emission from the merging cluster Cygnus A. We use 2.2 Msec Chandra and 40 ksec XMM-Newton archival datasets to map the thermodynamic properties of the intracluster gas in the merger region between the two sub-clusters in the system. These maps exhibit complex intracluster medium (ICM) structure and temperature fluctuations that imply significant heating along the merger axis. Possible sources for this heating could include the shock from the ongoing merger, past activity of the powerful AGN in the core, or a combination of both. To distinguish between these scenarios, we compare the observed X-ray properties of Cygnus A with simple, spherical cluster models to quantify the morphology and amount of heating in the merger region. The spherical models for the two sub-clusters are constructed using azimuthally averaged density and temperature profiles determined from the data neglecting the merger region. These models for the “undisturbed" sub-clusters were then folded through the MARX instrument simulators to produce realistic mock Chandra observations. The thermodynamic properties in the merger region from these mock X-ray observations were used as a baseline for comparison with the actual observations. This analysis identifies two components in the heated ICM, a series of 3-4 keV temperature peaks presumably associated with past episodic AGN activity, and a smooth, large-scale temperature excess attributed to the ongoing merger. These features are also seen in the XMM data. If attributable to the central AGN, the location and strength of these features imply that Cygnus A has been active for the past 400 Myr injecting a total of 10^60 erg into the merger region. This value corresponds to ~30% of the energy deposited in the same region by the merger shock. We conclude that the contribution due to AGN outbursts can be a significant fraction of the total energy deposited in the ICM over a cluster’s lifetime.