Joseph Callingham
Sydney Institute for Astronomy
University of Sydney
Tuesday, December 15, 1:00pm – AB Lounge

Abstract:  Gigahertz-peaked spectrum (GPS) and compact steep spectrum (CSS) sources have been hypothesised to represent an early stage of radio galaxy evolution. However, such an interpretation is contentious as it is possible that these sources are not young but are confined to a small spatial scales due to a high density medium. One of the main reasons there has not been resolution between these two competing hypotheses is because the absorption mechanism responsible for the turnover in their radio spectra still ambiguous since the spectra of these sources below the turnover has not been well enough sampled to date.

The Murchison Widefield Array (MWA) has conducted an all-sky survey at low radio frequencies (73 to 230 MHz). This survey provides an unparalleled number of GPS and CSS sources with broad spectral coverage below the turnover. In this talk I will outline the survey, present results of spectral modelling of these sources and discuss the impact such a frequency domain has on our understanding of the absorption mechanism. In particular, I will highlight the modelling of an extreme GPS source that has the steepest known slope below the turnover and smallest spectral width of any known GPS source. I will demonstrate that the MWA all-sky survey has identified a large population of GPS sources that have ceased activity, and will show that a portion of the ultra-steep spectrum source population will be composed of GPS sources in a relic phase.