On the location of X-ray peaks and dominant galaxies in clusters

Abstract

We analyze the structure of the X-ray emission of a sample of 22 Abell clusters of galaxies with a cD in their centre, observed with the ROSAT PSPC. Utilizing the multi-scale power of the Wavelet Transform we detect significant (~ 50 h^{-1} kpc) offsets between the large scale centroid and the peak of X-ray emission. Despite the uncertainties on the satellite pointing, the X-ray to optical correlation indicates a likely association between the X-ray peak and the dominant galaxy. We develop a model in which the offset is produced by small amplitude oscillations of the cD galaxy around the bottom of the cluster potential well and successfully compare it to the observed distribution of offsets. Within this scenario the offsets are not due to dynamic instabilities and the number of structured clusters is greatly reduced.