EXTRAGALACTIC RADIO OBSERVATIONS AT LOW FREQUENCIES: MEGAPARSEC JETS AND MERGING GALAXY CLUSTERS

Abstract

The radio jets from active galactic nuclei (AGN) can not only influence the evolution of the entire galaxy, but they can also extend up to many Mpc. Furthermore, they are common throughout galaxy clusters, influencing properties of the intra-cluster medium through the injection of relativistic particles. In this thesis I present deep radio observations using the LOw Frequency ARray (LOFAR), along with ancillary telescopes, to explore radio galaxies and merging clusters. Chapter 1 introduces galaxies, AGN and properties of their corresponding radio jets. Chapter 2 introduces galaxy clusters, their basic thermal and non-thermal properties, and highlights the advantage of radio observations to understand their phenomenology. Chapter 3 introduces radio astronomy, observing with dishes and phased arrays, and gives an overview of a facet based calibration scheme required to correct for direction dependent and ionospheric effects. Chapter 4 presents the discovery of a new giant radio galaxy (GRG), found in an ongoing survey with the LOFAR telescope: the Multifrequency Snapshot Sky Survey (MSSS). Chapter 5 continues the analysis of this new GRG by presenting deep follow up observations using LOFAR and the Giant Meter-wavelength Radio Telescope (GMRT). This new GRG extends for 40′on the sky, which at a redshift of 0.0545 gives a total projected physical size of 2.5 Mpc. It is thought to be very old (108 years), having attained its large size by growing in a low density environment. Chapter 6 presents deep LOFAR observations of the massive merging galaxy cluster Abell 1682. These high resolution (5′′) and low frequency (150 MHz) observations detect new filamentary structures not seen at higher frequencies, which are thought to be the tails from moving radio galaxies. Previous radio studies have speculated that Abell 1682 is the host of an Ultra Steep Spectrum Radio Halo (USSRH). These new observations show areas of steep spectrum emission, but seemingly associated with the tails of an inactive radio galaxy. An initial analysis of LOFAR data at lower frequencies (44 MHz) suggests that this steep spectrum emission extends beyond the associated radio galaxy tails, indicative of a diffuse radio halo between the two sub-clusters centre of masses. In such a scenario, mechanisms favour the re-acceleration of old mildly relativistic electrons to radio-emitting relativistic energies as a result of turbulence injected in the wake of the merger event. Chapter 7 presents some closing remarks and thoughts on future prospects with LOFAR.

Date of Award	1 Aug 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Keith Grainge (Supervisor) & Anna Scaife (Main Supervisor)