Speaker
Description
Recently, the ASKAP POSSUM and MeerKAT surveys revealed an apparent lack of radio source counts in the Fornax galaxy cluster field. The sources in this patch of sky also appeared to be less polarised. These observations are peculiar and could be important signatures of depolarisation on galaxy cluster scales. In this work, we quantified the effects on polarisation of radio point sources behind a large-scale intracluster shock. Our ray-tracing calculations revealed that, generally, bright sources do not experience any significant changes in polarisation, whereas faint sources either get severely depolarised or enhanced as their radiation propagates through the intracluster medium. Notably, most of the dim sources behind the shock gain linear polarisation. This is because the gas and magnetic fields are highly compressed within the shock, causing it to be more linearly polarised than the surrounding medium. We also carried out a magnetohydrodynamic FLASH simulation of an in-falling subcluster into a main cluster and found a substantial increase in the local Faraday rotation measures behind the shock front. These effects would impact the interpretations of radio observations, particularly with BURSTT and SKA-Low, where the polarisation bias in faint sources must be corrected for in the statistical analyses of dense rotation measure grids.
| Section | Galaxy/Extragalactic |
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