Observations of Abell 4059 with Chandra, HST and VLA: unraveling a complex cluster/radio-galaxy interaction

Abstract

(abridged) We present a detailed reanalysis of the Chandra data for the galaxy cluster Abell 4059 and its central radio galaxy, PKS2354-35. We also present new 1.4GHz and 4.7GHz CnB-array radio data from the Very Large Array (VLA), as well as a short archival WFPC2 image from the Hubble Space Telescope. The presence of a strong interaction between this radio galaxy and the intracluster medium (ICM) was suggested by Huang & Sarazin (1998) on the basis of a short observation by the High Resolution Imager on ROSAT, and confirmed in our preliminary analysis of the Chandra/ACIS-S data. In particular, X-ray imaging clearly shows two cavities within the ICM that are approximately aligned with the radio-galaxy axis. However, using our new radio maps we fail to find a detailed correspondence between the 1 arcmin scale radio-lobes and the ICM cavities. This suggests that the cavities are ``ghosts'' of a previous burst of powerful activity by PKS 2354-35. We also examine the nature of the central asymmetric ridge (or bar) of X-ray emission extending for 30kpc south-west of the cluster center that has been noted in these previous analyzes. We find the ridge to be denser and cooler than, but probably in pressure balance with, its surroundings. The thermal evolution of this structure seems to be dominated by radiative cooling, possibly enhanced by the radio-galaxy ICM interaction. We discuss several possible models for the formation of this SW ridge and find none of them to be entirely satisfactory.