Summary of observational results

There is clear evidence of a vigorous and complex radio-galaxy/cluster interaction between PKS2354-35 and A4059. Prior to the analysis presented in this paper, the known facts relevant to this interaction were:

1. There are two large ICM cavities approximately aligned with the axis of the radio galaxy. Huang & Sarazin (1998) and, later Heinz et al. (2002), showed that the radio source, as defined in the A- and B- array 4.8GHz and 8.5GHz VLA observations of Taylor et al. (1994) extends into the NW cavity, but does not extend to (or even point at) the SE cavity.
2. There is an offset between the center of the axis connecting the two cavities and the galactic nucleus. One is given the impression that, assuming the cavities were created symmetrically by the radio galaxy, they have subsequently ``drifted'' in a NE direction.
3. There is a bright ridge of emission extending from the center of the cluster in the SW direction. This ridge terminates about 25kpc to the SW of the center in an abrupt edge.

To this, we can now add the following informations:

1. VLA/CnB-array data taken at 1.4GHz, which is much better matched to detecting arcmin-scale structures than the previous radio data, still fails to detect any radio emission associated with the SE X-ray cavity.
2. There is no indication that the gas around the X-ray cavities is any hotter or higher entropy than the ambient gas. In other words, there is no evidence for a strong (or even moderately weak) shock surrounding the X-ray cavities.
3. The SW ridge appears to be in approximate pressure balance with the ambient material and is X-ray bright because of its lower temperature and higher density. The radiative cooling time in this structure is much shorter than that of the surrounding ICM, becoming as short as 100Myr (compared with a general ``core'' cooling time of greater than 500Myr).
4. There is a robust metallicity gradient within the cluster, with high metallicity (approaching solar) in the cluster center and then declining by a factor of 2 beyond 50kpc. This is reproduced in both the annular (i.e. projected) and deprojected spectral study. The presence of a central depression in the metallicity profile is suggested by single temperature fits to either the projected or deprojected spectra. However, the reality of this feature is unclear (see above for details).
5. HST/WFPC-2 imaging reveals that the cD galaxy and host of PKS2354-35, ESO349-G010, displays a prominent 5kpc dust lane oriented roughly perpendicular to the radio-axis. This suggests that it has accreted a dust rich companion galaxy in the past $10^8{\rm\thinspace yr}$ or so.

In this section, we discuss the constraints that these observations place on the nature of the interaction.