Deep radio studies of galaxy clusters at long wavelengths

Abstract

Observations at radio wavelengths continue to confirm the presence of extragalactic magnetic fields and relativistic electrons in the Universe. Studies of galaxy clusters have revealed spectacular sources of diffuse radio emission associated with the intracluster medium, broadly known as radio relics and radio haloes. This thesis presents the results of deep observations of three merging galaxy clusters: Abell 3667, Abell 3266 and MACS J0025.4-1222 with two pathfinder instruments for the Square Kilometre Array – the Karoo Array Telescope (KAT-7) and the Giant Metrewave Radio Telescope (GMRT).

Observations of Abell 3667 and MACS J0025.4-1222 reveal new sources of diffuse radio emission – a mini-halo in Abell 3667 (detected with KAT-7) and a double-relic system in MACS J0025.4-1222 (detected with the GMRT). Examination of power scaling relations indicates that these new sources are consistent with established trends in the known population. KAT-7 also recovers strong residual emission from Abell 3266, following subtraction of compact sources. However, its nature is unclear, as residual emission remains that appears to be associated with a number of other cluster member sources.

In this thesis, I also present observations of a galaxy super-cluster field with the GMRT and the Low-Frequency Array (LOFAR). I derive the deepest differential source counts to-date at 325 MHz, which exhibit the familiar flattening at mJy flux densities, and also suggests a subsequent downturn below 308 ?Jy. This corresponds well with the flux density regime where this feature has been detected at 1.4 GHz. The LOFAR source counts do not yet achieve sufficient sensitivity to probe this regime, or recover
the flattening seen at 325 MHz.

Finally, I also apply rotation measure synthesis to the LOFAR data to search for polarized sources in the field. I detect one polarized source within the 6.5 square degree field investigated in this thesis, which is insufficient to probe the magnetic field strength and structure of the super-cluster using a grid of sources with known RMs.

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