Unifying the Radio Spectrum to Map the Magnetic Universe

  • Fernando Eustáquio Dantas Dos Santos

Student thesis: Phd


This thesis presents the results of observations at low frequencies using Karl G. Jansky Very Large Array (VLA), at P-band in order to investigate the pair of merging galaxy clusters A222 and A223. These clusters possess a remarkable filamentary connection between them. An alternative method for calibration of the VLA P-band data using LOFAR facet-calibration technique, was applied in order to minimise the ionosphere effects. Thereafter, I have worked on the search for diffuse emission in A222-A223 system. No diffuse emission was detected using VLA observations at P-band. Although, the values derived are consistent with the established scaling relations between radio-power and X-ray luminosity. Also, PyBDSF compiled a catalogued which was used in the derivation of the source counts at 368 MHz. A comparison with Super-Class observations made by GMRT at 325 MHz was done, in order to check the consistency of the values between VLA and GMRT at P-band. Because the bridge connecting both galaxy clusters, A222-A223, demonstrated to have a potential region for detecting polarised sources, this work aimed to search for them via Faraday rotation spectral cube analysis, specifically using Rotation Measure (RM) synthesis. A deep optical identification was performed using the Friends-of-friends algorithm in order to pick the sources located at the filamentary connection. A spectral map of the region of interest was built and analised. However, the best 3 sources available in the filament region, did no show any polarisation at 368 MHz. This work will also present an useful relationship between Sunyaev & Zel'dovich and rotation measure in order to estimate magnetic field strength in the ICM. The relationship was firstly tested using a ``fake'' galaxy cluster in order to check its reliability. As the results were consistent with the expected electron density, Compton y-Parameter and magnetic field values, for typical galaxy clusters as a function of their radius; the relationship was, then used for a sample of galaxy clusters taken from an old, but seminal, paper in this field written by Tracy Clarke (NRL). This paper measured Faraday rotation for radio galaxies in a number of well-known galaxy clusters using data from the VLA telescope. In particular, the effect of varying/marginalizing over the temperature of the electron gas is a key point for investigation in this work. The observations at high frequencies was performed using the Arcminute Micro-Kelvin Imager (AMI) radio telescope for a sample of 12 galaxy (Clarke) clusters. The Clarke clusters sample were, then used to estimate the magnetic field strength in ICM regions away from the cluster's core. From the initial 12 galaxy clusters, only 5 presented a well-defined SZ negative contours. The results were analysed and showed good consistency with the expected values of the magnetic field as a function of the cluster's radius.
Date of Award1 Aug 2019
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorKeith Grainge (Supervisor) & Anna Scaife (Main Supervisor)


  • Galaxy Clusters
  • Magnetic Fields
  • Faraday Rotation
  • AMI
  • VLA
  • Sunyaev & Zel'dovich Effect

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