An investigation of the radio emission mechanism in strongly lensed radio quiet quasars

Abstract

This thesis is part of an ongoing discussion as to the emission mechanisms of radio quiet quasars. Current models describe the possible emission mechanisms as either jetted or non‐jetted (Padovani, 2017) but recent studies have indicated that there is room for a mixture of physical processes that drive the radio emission (Hartley et al., 2021). Gravitational lensing is a tool which allows us to study faint radio quiet quasars at resolutions that would otherwise be impossible allowing compact structure around quasar cores to be resolved using VLBI. This thesis contains the analysis of 12 strongly lensed radio quiet quasars with significant radio detections from the VLA interferometer where the detection rate was 12 sources of 22 detected with a detection limit of∼ 10μJy (∼ 2.5σ). Of these sources; the radio emission of eight of them is likely to be dominated by star formation, one source is likely AGN dominated in the radio, and three sources are a possible mix of star formation and compact AGN activity. From the sample of 12, only three sources have FIR detections available therefore the other nine sources have FIR flux upper limits and thus upper limits on the QIR which determines if a galaxy is star forming or not. Two of the RQQs, SDSSJ0820+0812 and SDSSJ1128+2402, have radio spectral indexes of ‐1.020±0.392 and −0.726 ± 0.200 respectively which is consistent with synchrotron radiation which is likely to originate in small scale AGN jets. One source, SDSSJ0941+0518, has a spectral index of −0.113 ± 0.158 which in indicative of thermal free‐free emission (Bremsstrahlung radiation) which could be due to a thermally heated torus about the SMBH. SDSSJ0820+0812, SDSSJ0941+0518, and SDSSJ1128+2402 have inferred dominant radio emission mechanisms of star formation from the FIRC but their spectral indexes imply otherwise giving rise to a discrepancy between the RQQ emission mechanisms inferred from the radio spectral index and their position on the FIRC.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Neal Jackson (Supervisor) & Rob Beswick (Supervisor)