Conclusions

We have presented CXO observations of Abell 4059. While the ICM appears smooth and relaxed on large scales, it shows complex morphology in the core region which is likely the result of interaction between the ICM and the central FR-I radio galaxy PKS2354-35. As was suggested by HS, PKS 2354-35 appears to have inflated two large cavities in the ICM. Together with a central bar-like structure, these cavities produce an hour-glass like morphology which can be readily understood as being due to a radio cocoon expanding into the ICM. While clear correspondence exists between the NW cavity and the NW radio lobe, the SE cavity is much larger than the SE lobe, suggesting that this could be a `missing link' between cavities with and without visible radio lobes.

The absence of sharp edges in the brightness images and of large temperature jumps implies that PKS2354-35 is not driving a strong shock into the ICM. We suggest that it is in the weak-shock/compression-wave phase identified in the hydrodynamic simulations of RHB. Dynamical estimates give a time averaged kinetic source power of at least $L_{\rm kin} \gtrsim 3\times 10^{44}\hbox{${\rm\thinspace erg}{\rm\thinspace s}^{-1}\,$}$, while estimates based on the current radio luminosity indicate a source power of $L_{\rm kin} \lesssim 7\times 10^{43}\hbox{${\rm\thinspace erg}{\rm\thinspace s}^{-1}\,$}$. We suggest that this source has faded by a significant amount (and possibly from an FR-II phase) during the past $10^8{\rm\thinspace yr}$.