Open Access Te Herenga Waka-Victoria University of Wellington
thesis_access.pdf (28.19 MB)

A Radio View of the Bullet Cluster from 100 MHz to 9 GHz

Download (28.19 MB)
posted on 2021-12-08, 12:43 authored by Srinivasan, Raghav

We investigate a sample of 10 massive galaxy clusters for diffuse synchrotron emission. The shortlisted clusters are drawn from a sample of clusters observed with the South Pole Telescope (SPT) shown to have high Sunyaev-Zeldovich (SZ) signals.They are analysed for diffuse emission from the results of the Australia Telescope Compact Array (ATCA) archival data reduction. The focus then is on the cluster with the most prominent diffuse emission - the Bullet cluster. We used the Murchison Widefield Array Commissioning Survey (MWACS) data in conjunction with the ATCA images to derive the spectral behaviour of the Bullet cluster from 0.118 GHz to 8.896 GHz. In particular, we study the spectral properties of the known radio halo and radio relic. We search for spectral bending of this diffuse emission as seen in other clusters like the Coma cluster, A2256, A521 and A3256.  We detect the radio relic at all frequencies in the cluster periphery. Polarised flux is detected for the relic at all frequencies except at 1.344 GHz and as expected the percentage polarisation increases with frequency. Our spectral index values of -1.08 ± 0.02 and -1.74 ± 0.22 for 2 regions of the radio relic agreed with the literature. We detect spectral flattening for a region in the radio relic at 4.532 GHz. This is a common spectral characteristic for a radio galaxy. This suggests that the source could be a recently dead radio galaxy. We discuss a scenario in which a dead radio galaxy supplying seed electrons for reacceleration and a merger process providing the required energy for the diffuse radio relic. We detect the radio halo at all frequencies and we derive a spectral index of -2.11±0.03 using our ATCA flux measurements. Our individual flux measurements at 1.344 and 2.1 GHz agree with the literature. However, we get a steeper ATCA spectral index value for the radio halo as compared to the existing value in the literature. We observe spectral flattening of the radio halo in the Bullet cluster at low frequencies between 0.180 GHz and 1.3 GHz. This is similar to the spectral property of the halo in clusters like the Coma cluster, A521 and A3256.


Copyright Date


Date of Award



Te Herenga Waka—Victoria University of Wellington

Rights License

Author Retains Copyright

Degree Discipline


Degree Grantor

Te Herenga Waka—Victoria University of Wellington

Degree Level


Degree Name

Master of Science

ANZSRC Type Of Activity code

970102 Expanding Knowledge in the Physical Sciences

Victoria University of Wellington Item Type

Awarded Research Masters Thesis



Victoria University of Wellington School

School of Chemical and Physical Sciences


Johnston-Hollitt, Melanie