Hot and cold bubbles in M87

The X-ray data obtained with XMM-Newton are used to investigate the complex structure of the gas in the atmosphere of the Virgo cluster around M87. We construct a simple model for the temperature and density distribution. This model implies that the cumulative mass of the cluster gas is a power law of its entropy index, kTn^-2/3, similar to the Hydra cluster. This supports the idea that such power laws are a direct consequence of gas cooling in a gravitational potential. In the cluster atmosphere, hot bubbles of gas injected by the active galactic nuclei (AGN) are rising buoyantly. We estimate the age of these structures from the synchrotron radio data and find that this `radiative age' is consistent with the estimated dynamical time-scale. However, this requires a spatial separation of the relativistic particles from the magnetic field. The age estimates suggest an activity cycle of the AGN in M87 of roughly 10⁸ yr. We show that the largest radio structures are consistent with being the remnants of buoyant bubbles injected by the AGN during an even earlier activity cycle. The wakes behind the currently rising hot bubbles uplift cold gas from the cluster centre. Using a simple model for the trajectory of the cold gas, we demonstrate that the observations by XMM-Newton of a mix of hot and cold gas in the cluster atmosphere in the vicinity of the radio structure can be explained in this scenario. This may also explain the ridges of enhanced X-ray emission from cold gas observed with Chandra.