Multi-wavelength study of large-scale outflows from the Circinus galaxy

Ebrahim, Rozeena
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The Circinus galaxy is a composite starburst/Seyfert galaxy that exhibits radio lobes inflated by kpc scale outflows along its minor axis. Its proximity (4 Mpc) makes it a unique target to study the physical nature of these outflows. We investigate if they originate from nuclear star formation activity or if they are jets from an active galactic core. The MeerKAT radio observations allow us to study the morphology of the arcminute lobes of the Circinus galaxy. In this work, a multi-wavelength analysis of this system is conducted using the available MeerKAT observations and Fermi-LAT data, to aid in the understanding of the origin of these structures. We found that the shell of the radio lobes is likely created by a weak shock that swept up and accelerated electrons in the interstellar medium to produce the edge-brightening effect. The MeerKAT spectral index map of the lobes also challenges previous evidence made against the starburst model. Our Fermi-LAT analysis results support a starburst origin for the GeV emission of Circinus due to the CR-ISM interaction and a proton calorimeter model for Circinus. However, we also show that the flux decline of SN1996cr as the origin of the GeV emission of Circinus cannot be ruled out. These results are also compared to the star-formation driven Fermi bubbles in the Milky Way, which have been observed in both theγ-ray and the radio bands, to determine physical similarities between these structures
A dissertation submitted to the Faculty of Science at the University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Physics, 2021