Observations and Investigations of Two Gravitationally-Lensed Quasars

  • Yik Lok Wong

Student thesis: Master of Science by Research


This thesis presents enhanced Multi Element Remotely Linked Interferometer Network (e-MERLIN) data on two gravitationally-lensed quasars, CLASS B0850+054 and HE 0435-1223. Observations were made with e-MERLIN and data are calibrated with the Astronomical Image Processing System AIPS. CLASS B0850+054 was observed with e-MERLIN at 5 GHz in search of the central image, and set constraints on the inner mass profile of the lensing galaxy. Although no central image is detected, the detection limit of the observation sets a limit on the flux ratio between the brightest component and the central image. By investigating the Keeton (2003) sample for early-type galaxies and carrying out mass modelling, we have obtained a set of Nuker-law parameters that is able to reproduce the observed source separation and flux ratio. In the next step of modelling, we optimize for the values of convergence κb and source separation s while varying the break radius rb and inner power-law index γ to reproduce the observed data. In addition, the black hole mass is also varied and the sharpness of break α is fitted for. Results show that either the galaxy has a small core radius and a near-isothermal core, or that the central image is heavily demagnified by the central supermassive black hole (SMBH) and can never be detected. For the case of the lensed radio-quiet quasar (RQQ) HE 0435-1223, it was observed with e-MERLIN at 1.5 GHz. We suggest that the emission mechanism of this source is star formation around the central SMBH. The map of HE 0435-1223 shows a non-detection of the source, which indicates that the background source size at 1.5 GHz is larger than that of the beam size 408 × 106 mas2. This corresponds to an upper limit on the brightness temperature of 1.74×103 K at the detection limit of 34.89 μJy beam−1. As a low brightness temperature (< 104 K) is expected in a star-forming galaxy, we suggest that star formation is powering the radio emission in HE 0435-1223.
Date of Award1 Aug 2024
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorNeal Jackson (Supervisor) & Eamonn Kerins (Supervisor)


  • Radio Interferometry
  • Gravitational Lensing
  • Central Image
  • Active Galactic Nuclei (AGN)
  • Star Formation

Cite this