Evidence for merging in the Centaurus cluster

We present a two-dimensional map of the gas temperature distribution in the Centaurus cluster, based on Advanced Satellite for Cosmology and Astrophysics (ASCA) observations derived using a novel approach to account for the energy-dependent point-spread function. Along with a cool region centered on NGC 4696, asymmetric temperature variations of moderate amplitude are detected. The hottest region roughly coincides with the position of the second-brightest galaxy, NGC 4709, known to be the dominant galaxy of one of the subgroups in the Centaurus cluster. ROSAT images show faint surface brightness emission also centered on this galaxy. The imaging and spectral results suggest that a subcluster centered on NGC 4709 is merging with the main cluster centered on NGC 4696, in agreement with earlier suggestion that these two systems are located at the same distance, despite their different line-of-sight velocities.