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Powerful radio galaxy Cygnus A with AGN core (centre), jets and hotspots on lobes. Such detailed images at low frequencies are currently not possible due to angular resolution limitations. (Image courtesy of NRAO/AUI).

Powerful radio galaxy Cygnus A with AGN core (centre), jets and hotspots on lobes. Such detailed images at low frequencies are currently not possible due to angular resolution limitations. (Image courtesy of NRAO/AUI).

The infalling of matter into the central supermassive black hole in a massive galaxy causes the nuclear region to become extremely luminous, an object known as an Active Galactic Nucleus or AGN. The jets from AGNs transport matter outwards. Where these jets meet the intergalactic medium, bright spots called hot-spots are formed and are seen as part of radio galaxy lobes. At high radio frequencies (>1GHz), the brightness of hotspots decreases with increasing frequency, but at low radio frequencies (~100MHz) the behaviour is poorly understood, since only a small number of objects have been studied in detail. Until now, a large study of hotspots at low frequencies has not been technically feasible due to the challenges of achieving sufficiently high angular resolution to separate the hotspot and lobe emissions. The Murchison Widefield Array (MWA), operated by ICRAR-Curtin, is a low-frequency radio interferometer unparalleled in its wide field of view and its imaging fidelity, making it an excellent instrument to study powerful radio galaxies at low radio frequencies. Although a remarkably flexible instrument, its angular resolution does not exceed 1 arcminute.

However, we have shown that we can use this instrument to probe the sub-arcsecond properties of sources via the phenomenon of Interplanetary Scintillation (IPS). Sources which have compact components will change rapidly in brightness (on timescales of ~1s) due to turbulence in the interplanetary medium. Applying this well-studied technique to the wide field of view of the MWA allows us to identify compact components in thousands of objects. Using this information, combined with complementary catalogues, the presence of secondary compact components (hot spots) and their brightness can be inferred. This will allow us to perform a survey of radio galaxies, identifying hotspots, and use the resulting information to understand their relationship with their host radio galaxies.

3C33 as it appears in TGSS, a low frequency survey. There appears to be a hotspot in the Southern lobe, but the resolution is not sufficient to separate lobe and hotspot emission

3C33 as it appears in TGSS, a low frequency survey. There appears to be a hotspot in the Southern lobe, but the resolution is not sufficient to separate lobe and hotspot emission.

The powerful technique of IPS on wide field-of-view is an important new development, and its full implications in the era of the Square Kilometre Array are not yet fully appreciated. There is therefore a unique opportunity for a student to contribute to the development of a technique which can directly inform SKA design studies, and ultimately be leveraged to perform new science with the SKA. The project would require a student with an interest in confronting technical challenges in order to perform novel science. Experience in radio astronomy or big data computation would be beneficial. The project can be tailored to suit the individual candidate’s interests, whether they be in Radio Galaxies, SKA science, or high-performance computing.

Co-Supervisors

Dr John Morgan

Research Fellow

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A/Prof Jean-Pierre Macquart

Associate Professor

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