Shockwaves of galaxy cluster merger seen as bridge in radio data
As part of S-PASS (S-band Polarization All Sky Survey), a single-dish survey of the total intensity and polarised continuum emission of the entire southern sky, observations at 2.3 GHz with the Parkes Radio Telescope have now revealed a ‘bridge’ of unpolarised synchrotron emission (stretching some one third of a degree on the sky) between the centre of cluster Abell 3667 and its outlying relic regions. This is the first significant detection of such a connecting structure associated with both a cluster relic and X-ray emission from the cluster centre.
In a paper accepted for publication in MNRAS, the team around CSIRO lead author Ettore Carretti, including our CAASTRO Directors Bryan Gaensler and Lister Staveley-Smith, carefully stripped their single-dish data from confounding signals, using nine hours of observations with the Australia Telescope Compact Array in Narrabri at the S-PASS frequency for compact source subtraction. The detection of the two radio relics were confirmed by previous data sets from the Molonglo Observatory Synthesis Telescope (MOST).
The researchers interpret their data as an indication that Abell 3667 shows the aftermaths of a collision between two merging galaxy clusters that generates outgoing shock waves. The observed synchrotron emission ‘bridge’ is thought to be the post-shock turbulence trailing the shock. Follow-up observations at other frequencies are required to rule out other mechanisms, for instance hadronic secondary models of cosmic-ray acceleration in the post-shock region.
E. Carretti, S. Brown, L. Staveley-Smith, J. M. Malarecki, G. Bernardi, B. M. Gaensler, M. Haverkorn, M. J. Kesteven, S. Poppi in MNRAS 2013