Thesis title: A Southern Sky Catalogue of Radio Haloes and Relics with the Murchison Widefield Array (MWA)
My main field of research is concerned with diffuse, non-thermal radio emission within and around galaxy clusters. The work I do is in detection and characterisation of such emission, utilising telescopes such as the MWA, the Australia Telescope Compact Array, and the Australia Square Kilometre Array Pathfinder. In general, the work is done in the image plane using various source-finding techniques—both automated and in a more manual sense. Cluster haloes and relics are the two main types of sources we are interested in—thought to form from shocks and turbulence within the clusters and trace the merger history or dynamical state of the cluster. These sources are important in uncovering the nature behind cluster magnetic fields, perhaps eventually answering the question of their origin.
To date, I have published observations of large-scale radio emission in and around clusters:
- A follow-up of the remnant radio galaxy associated with the lenticular galaxy NGC 1545 (Duchesne & Johnston-Hollitt, 2019). In this work we confirmed the diffuse emission initially detected by Hurley-Walker et al. (2015) as being a remnant radio galaxy associated with NGC 1534 with archival and new ATCA observations and recently released MWA survey data, showing it to have a characteristic spectral energy distribution of remnant sources and a non-active host. Investigation into its polarimetric properties via wideband rotation measure synthesis found potential intrinsic polarization from the radio lobes.
- Detection of an ultra-steep spectrum (USS), extended object in Abell 1127 and the description of my MWA phase 2 data processing pipeline (Duchesne et al., 2020), including spectral modelling of the USS source and description of new methods for handling MWA phase 2 imaging data including image-based flux scaling and methods to handle a re-projected point-spread function—a problem largely unique to widefield MWA data.
- Detection of a double relic system in SPT-CL J2032-5627 using early science ASKAP data (Duchesne et al., 2021). This work involved imaging of new ASKAP data products and development of a pipeline to produce quick results with archival ASKAP data, with a focus on diffuse source imaging. Additionally, we showed the power of ASKAP (and even limited ATCA data, if in a compact configuration) in detecting such emission in widefield surveys.
Future works will focus on a larger sample of diffuse, steep-spectrum cluster sources detected with the MWA, and followed up with both the MWA phase 2 and recent survey data from ASKAP.
Additional work during my PhD has been focused on contributing to other work in the realm of large-scale radio emission, including the study of the cluster system Abell 3391-95 (Brüggen et al., 2020). The system had a bridge of emission detected in recently released eROSITA images (Reiprich et al., 2020), though we were unable to detect the bridge via radio emission using ASKAP at 900 MHz and a set of comparatively less sensitive MWA images below 300 MHz. This work instead showed a host of extended radio sources in an around the clusters and a higher density than expected.
My MSc was completed at the beginning of 2017 under Professor Melanie Johnston-Hollitt at Victoria University of Wellington (VUW). This work made use of André Offringa’s deep MWA image of the EoR0 field (Offringa et al. 2016), which involved detecting halo and relic emission from clusters within the 45 degree by 45 degree field (Duchesne et al., 2017).
Additionally, I have worked with Dr. Stephen Curran at VUW investigating neutral hydrogen absorption profiles of distant galaxies.
Brüggen M. et al., 2020, A&A, in press
Duchesne S. W. et al., 2017, PASA, in press
Duchesne S. W. & Johnston-Hollitt M., 2019, PASA, 36, e050
Duchesne S. W. et al., 2020, PASA, 37, e037
Duchesne S. W. et al., 2021, PASA, 38, e005
Hurley-Walker N. et al., 2015, MNRAS, 447, 2468
Offringa A. R. et al., 2016, MNRAS, 458, 1057
Reiprich T. H. et al., 2020, A&A, in press
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