High-Resolution Maps of FRII DRAGNs

  • Katie Lyn Hesterly

Student thesis: Phd


Supermassive black holes at the centre of galaxies are strongly linked to relativistic plasma outflows seen in nearly 10% of all active galaxies. These outflows may be responsible for producing the most energetic particles in the universe, and are known to influence the formation and evolution of structure in the universe. While it is clear that jets are transporting matter and energy to great distances, the mechanism for doing so is poorly understood. A longstanding problem in jet physics is the appearance of two flavours of jets. Entrainment appears to play a role in sources with a higher surface brightness closer to the central region. For edge-brightened sources like Cygnus A, what mechanism allows them to sustain a well-collimated relativistic jet out to many kiloparsecs? Previous studies of kiloparsec-scale jets were limited by sensitivity, bandwidth, and resolution. Modern interferometers offer a chance to observe jets across many frequencies with excellent sensitivity and resolution. The work presented in this thesis is part of the e-MERLIN Extragalactic Jets Legacy Project which seeks to probe sub-arcsecond structures at 1.5 and 5 GHz. The project aims to shine new light on key areas such as: (1) What are the transverse structures in the jet like?; (2) Is there any evidence for a spine-sheath along the jet?; and (3) Can we link acceleration to areas of brightening? Presented here are high resolution and sensitivity radio maps of two powerful FRII quasars - 3C334 and 3C263, and one powerful FRII radio galaxy - Cygnus A, with observations from the combined e-MERLIN and JVLA arrays. The 1.5 GHz radio map of 3C 334 is the highest-resolution map to date. The improved maps reveal new knots along the jet and hotspots previously unresolved in the next best resolution maps. Within the counterjet "head" feature, we identify a centrally placed secondary hotspot. While this was identified in previous maps, the feature did not qualify as a hotspot at lower resolutions. Details of the radio structure and an analysis of the apparent jet opening angle is discussed. A spectral index map created at 1.5 and 5 GHz (matched to a common resolution) is provided. Evidence in support of jet precession is outlined based on the alignment of many distinct features within the quasar's lobes. The e-MERLIN+JVLA 1.5 GHz map of 3C263 has revealed a strikingly straight, narrow, and mostly unresolved jet. A previously unresolved knot close to the core is identified. The high-resolution maps reveal a narrow deflecting jet entering the east hotspot. At VLA resolution the feature was considered a part of the jet due to the orientation and placement but was significantly less resolved. The hotspots in the west lobe are resolved into complex smaller features. The e-MERLIN maps of Cygnus A provided a unique resolution to its hotspots and jet at 1.5 and 5 GHz. In both observations the transient observed by the JVLA was detected at a position of alpha =19:59:28.328, delta = +40 4401.913 at 1.5 GHz, and alpha = 19:59:28.3227, delta = +40 44 01.9280 at 5 GHz. The SED indicates the flux at each frequency (S1.5 = 5.2+/-2.2 mJy and S5 = 4.05+/-0.5 mJy) is consistent with the estimated flux (~3-4 mJy). At 5 GHz a structure extending ~0.10 from the centre of the core and perpendicular to the direction of the jet is imaged. This may be support for the higher frequency JVLA detection of a torus, but sidelobes around the core reduce our confidence in the detection .
Date of Award1 Aug 2021
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorIan Browne (Supervisor) & Paddy Leahy (Supervisor)


  • AGN
  • Extragalactic jets
  • Quasars
  • Radio Galaxies
  • VLA

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