2014-A, 128T

Testing Predictions for Diffuse Radio Emission in Massive Galaxy Clusters

Authors: Dr. Melanie Johnston-Hollitt, Dr. Gianfranco Brunetti, Dr. Rossella Cassano, Siamak Dehghan, Prof. Daniele Dallacasa, Dr. Luke Hindson, Dr. Natasha Hurley-Walker, Dr. Ruta Kale, Rowan Miller, Sara Shakouri, Dr. Tiziana Venturi, Dr. Cathie Zheng

Abstract: We propose to undertake a point and track study of 25 massive (M > 4x10^14 solar masses) galaxy clusters with declinations between 0 and -65 degrees drawn from the Planck SZ Cluster Catalogue. This sample will be matched to the resolution of the MWA and thus limited to z less than 0.13 and will be used to search for as yet undetected radio halos and relics using the MWA's unique instrumental niche for low frequency observations in the Southern Hemisphere. With such a mass-selected sample in hand, we will be able to undertake an unbiased examination of radio halo and relic generation in galaxy clusters including correlation of halos and relics to dynamical state and undertake the first widespread search for the predicted population of ultra-steep spectrum radio halos expected to be only detectable below 300 MHz.

The Horologium-Reticulum Supercluster as a cosmic laboratory to investigate the role of environment on the radio source population

Authors: Dr. Melanie Johnston-Hollitt, Siamak Dehghan, Dr Luke Hindson, Dr Natasha Hurley-Walker, Dr Emil Lenc, Rowan Miller, Sara Shakouri, Dr. Cathie Zheng

Abstract: We propose to use the MWA to map the 180 square degree area of the Horologium-Reticulum supercluster (HRS) down to the confusion limit at 95, 155 and 215 MHz. Combined with our existing extensive spectroscopic data and 1.4 GHz imaging, this will provide an unprecedented opportunity to examine the low frequency radio source population as a function of environment from filaments and groups to rich clusters. As a secondary science goal we will examine the rotation measure across this field from known regions of diffuse polarized emission in the northern clusters. We are particularly fortunate in these observations as the HRS is suitable away from the Galactic plane close to the known MWA polarization calibrator, PMN J0351-2744, allowing excellent polarization characterization of the field.

Synchrotron emission on cluster and supercluster scales: the Shapley supercluster

Authors: R. Kale, S. Bardelli, G. Brunetti, R. Cassano, D. Dallacasa, K. S. Dwarakanath, S. Giacintucci, M. Johnston-Hollitt, M. Rossetti, T. Venturi

Abstract: The inter-galactic medium (IGM) that permeates the space between individual galaxies through-out the large-scale structure of the Universe beyond the most massive clusters remains elusive. With 0.1-1 μG magnetic fields and electrons accelerated at the shocks due to infalling matter, the cosmic web is expected to be a source of synchrotron emission on scales of a few Mpc forming a ‘synchrotron web’. The unprecedented surface brightness sensitivity and short baseline uv-coverage of the Murchison Widefield Array in combination with the TIFR GMRT Sky Survey provides a unique opportunity to probe the synchrotron web.

We propose MWA observations of the Shapley supercluster (SSC) region. SSC consists of several merging clusters and galaxy groups forming a filamentary structure located at a mean redshift of 0.048. It is a unique candidate to find diffuse emission on cluster and supercluster scales. A wealth of information on SSC is available in this collaboration at frequency bands ranging from X-rays to low radio frequencies. The compact and extended radio galaxies, background radio sources and a radio halo in the SSC region are well known at several radio frequencies in the range 240 MHz - 5 GHz. The proposed observations with the MWA will be the first to explore radio emission on supercluster scales and lead to pathbreaking discoveries at low radio frequencies.