Abstract Details
| Name: Lijo Thomas George Affiliation: Raman Research Institute Conference ID: ASI2017_744 Title : Observations of radio halos and relics with the MWA Authors and Co-Authors : K. S. Dwarakanath (RRI) + MWA Collaborators Abstract Type : Reject Abstract Category : Thesis Abstract : Galaxy clusters are some of the largest (~Mpc) gravitationally bound objects in the Universe. In addition to luminous and dark matter, clusters contain hot (~10^6 K) gas which emit thermal X-ray bremsstrahlung radiation. A small fraction of galaxy clusters (~5%), also emit synchrotron radiation in the form of Mpc sized central radio halos or peripheral radio relics. This dearth of detection can be due to many reasons. Radiative losses cause a steepening in the radio spectrum of halos and relics at higher radio frequencies (>1 GHz). Furthermore, radio halos also show an empirical relation between the radio power of the halo at 1.4 GHz (P_1.4) and the X-ray luminostiy of the cluster (L_X). Therefore, less massive clusters will have correspondingly lower radio power which might be too weak to be detected by the current generation of radio telescopes. Another issue with high frequency measurements is that at low redshifts (z<0.1) the extended diffuse emission of radio halos and relics is likely to be resolved out due to the lack of short spacings needed to effectively image them. Thus, low frequency measurements are better suited to detect the diffuse radio emission in galaxy clusters. For these reasons we decided to observe 10 merging galaxy clusters using the Murchison Widefield Array (MWA) which is located in a radio-quiet zone in Western Australia because of which RFI is also not an issue with these measurements. The MWA operates in the frequency range 80-230 MHz. The 10 clusters where chosen from literature based on their high frequency measurements. They contain relics with or without radio halos. Our aim was to detect any possible halo emission that might have been missed by existing telescopes. Furthermore, we obtained the spectra of the halos and relics in the frequency range 80-1400 MHz. This is the first time spectra has been estimated over such a large frequency range. Additionally, in clusters where no halo was detected we placed upper limits to a possible halo emission. These limits are a factor of 10-50 below those expected from the Lx-P1.4 relation. The implication of these results to the models of halo formation are discussed. |