Cold fronts and multi-temperature structures in the core of Abell 2052

¹ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
e-mail: j.de.plaa@sron.nl
² Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 382 via Pueblo Mall, Stanford, CA 94305-4060, USA
³ Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands

Received: 11 June 2010
Accepted: 13 August 2010

Abstract

Context. The physics of the coolest phases in the hot intra-cluster medium (ICM) of clusters of galaxies is yet to be fully unveiled. X-ray cavities blown by the central active galactic nucleus (AGN) contain enough energy to heat the surrounding gas and stop cooling, but locally blobs or filaments of gas appear to be able to cool to low temperatures of 10⁴ K. In X-rays, however, gas with temperatures lower than 0.5 keV is not observed.

Aims. We aim to find spatial and multi-temperature structures in the hot gas of the cooling-core cluster Abell 2052 that contain clues on the physics involved in the heating and cooling of the plasma.

Methods. 2D maps of the temperature, entropy, and iron abundance are derived from XMM-Newton data of Abell 2052. For the spectral fitting, we use differential emission measure (DEM) models to account for the multi-temperature structure.

Results. About 130 kpc South-West of the central galaxy, we discover a discontinuity in the surface brightness of the hot gas which is consistent with a cold front. Interestingly, the iron abundance jumps from  ~0.75 to  ~0.5 across the front. In a smaller region to the North-West of the central galaxy we find a relatively high contribution of cool 0.5 keV gas, but no X-ray emitting gas is detected below that temperature. However, the region appears to be associated with much cooler Hα filaments in the optical waveband.

Conclusions. The elliptical shape of the cold front in the SW of the cluster suggests that the front is caused by sloshing of the hot gas in the clusters gravitational potential. This effect is probably an important mechanism to transport metals from the core region to the outer parts of the cluster. The smooth temperature profile across the sharp jump in the metalicity indicates the presence of heat conduction and the lack of mixing across the discontinuity. The cool blob of gas NW of the central galaxy was probably pushed away from the core and squeezed by the adjacent bubble, where it can cool efficiently and relatively undisturbed by the AGN. Shock induced mixing between the two phases may cause the 0.5 keV gas to cool non-radiatively and explain our non-detection of gas below 0.5 keV.