New insights into structure formation from XMM observations of merging clusters
Abstract
Hydrodynamical simulations predict that merger events strongly affect the physical characteristics of the intra-cluster medium (ICM). In particular the temperature structure is thought to be an excellent indicator of the cluster dynamical state and formation history. Spectro-imaging observations with XMM-Newton and Chandra now allow the building of precise temperature maps, enabling deeper investigation of the dynamical processes of cluster formation and the effect of the mergers on the ICM. We present new results from the XMM-Newton observations of our ongoing programme on merging clusters. To date three clusters have been observed, covering the temporal sequence from early to late stage mergers: A1750, A3921 and A2065. Using spatially-resolved spectroscopy of discrete regions, temperature and hardness ratio maps, we show that all three clusters display a complex temperature structure. In the case of A1750, a double cluster, we argue that the observed temperature structure is not only related to the ongoing merger but also to previous merger events. Using comparisons with numerical simulations and complementary optical data the highly complex temperature structure evident in A3921 is interpreted as an off-axis merger between two unequal mass components. Finally A2065 seems an excellent example of a "compact merger", i.e. when the centres of the two clusters have just started to interact, producing a shock in the ICM. These results illustrate the complex physics of mergers events The relaxation time can be larger than the typical time between merger events, so that the present day morphology of clusters depends not only on on-going interaction but also on more ancient formation history. We will also present preliminary results from a systematic study of temperature structure in a larger sample of 10 clusters.
- Publication:
-
35th COSPAR Scientific Assembly
- Pub Date:
- 2004
- Bibcode:
- 2004cosp...35.1831B