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Deep radio studies of galaxy clusters at long wavelengths

Deep radio studies of galaxy clusters at long wavelengths
Deep radio studies of galaxy clusters at long wavelengths
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.
University of Southampton
Riseley, Christopher John
f418e7cb-9709-4efd-a9a8-bfca84c7ea7b
Riseley, Christopher John
f418e7cb-9709-4efd-a9a8-bfca84c7ea7b
McHardy, Ian
4f215137-9cc4-4a08-982e-772a0b24c17e

Riseley, Christopher John (2016) Deep radio studies of galaxy clusters at long wavelengths. University of Southampton, Physical Sciences and Engineering, Doctoral Thesis, 304pp.

Record type: Thesis (Doctoral)

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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Published date: December 2016

Identifiers

Local EPrints ID: 405434
URI: http://eprints.soton.ac.uk/id/eprint/405434
PURE UUID: 378eecf1-83c4-4245-be24-e7df167f79e0

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Date deposited: 18 Feb 2017 00:23
Last modified: 13 Mar 2019 20:18

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