The large-scale shock in the cluster of galaxies Hydra A

Abstract

We analyzed a deep XMM-Newton observation of the cluster of galaxies Hydra A, focusing on the large-scale shock discovered as a surface brightness discontinuity in Chandra images. The shock front can be seen both in the pressure map and in temperature profiles in several sectors. The Mach numbers determined from the temperature jumps are in good agreement with the Mach numbers derived from EPIC/pn surface brightness profiles and previously from Chandra data and are consistent with M~1.3. The estimated shock age in the different sectors using a spherically symmetric point explosion model ranges between 130 and 230 Myr and the outburst energy between 1.5 and 3e61 ergs. The shape of the shock seen in the pressure map can be approximated with an ellipse centered 70 kpc towards the NE from the cluster center. We aimed to develop a better model that can explain the offset between the shock center and the AGN and give a consistent result on the shock age and energy. To this end, we performed 3D hydrodynamical simulations in which the shock is produced by a symmetrical pair of AGN jets launched in a spherical galaxy cluster. As an explanation of the observed offset of the shock center, we consider large-scale bulk flows in the intracluster medium. The simulation successfully reproduces the size, ellipticity, and average Mach number of the observed shock front. The predicted age of the shock is 160 Myr and the total input energy 3e61 erg. Both values are within the range determined by the spherically symmetric model. Matching the observed 70 kpc offset of the shock ellipse from the cluster center requires large-scale coherent motions with a high velocity of 670 km/s. We discuss the feasibility of this scenario and offer alternative ways to produce the offset and to further improve the simulation.