A detached double X-ray tail in the merging galaxy cluster Z8338 with a large double tail

Abstract

ABSTRACT When subhaloes infall into galaxy clusters, their gas content is ram pressure stripped by the intracluster medium (ICM) and may turn into cometary tails. We report the discovery of two spectacular X-ray double tails in a single galaxy cluster, Z8338, revealed by 70 ks Chandra observations. The brighter one, with an X-ray bolometric luminosity of 3.9 × 1042 erg s−1, is a detached tail stripped from the host halo and extended at least 250 kpc in projection. The head of the detached tail is a cool core with the front tip of the cold front ∼30 kpc away from the nucleus of its former host galaxy. The cooling time of the detached cool core is ∼0.3 Gyr. For the detached gas, the gravity of the once-associated dark matter halo further enhances the Rayleigh–Taylor instability. From its survival, we find that a magnetic field of a few μG is required to suppress the hydrodynamic instability. The X-ray temperature in the tail increases from 0.9 keV at the front tip to 1.6 keV in the wake region, which suggests the turbulent mixing with the hotter ICM. The fainter double X-ray tail, with a total X-ray luminosity of 2.7 × 1042 erg s−1, appears to stem from the cool core of a subcluster in Z8338, and likely was formed during the ongoing merger. This example suggests that X-ray cool cores can be displaced and eventually destroyed by mergers, while the displaced cool cores can survive for some extended period of time.