Boosting the performance of big dishes

A special kind of radio-wave receiver called a phased-array feed can make possible new kinds of research with large single-dish radio telescopes, tests led by CAASTRO researchers have shown.

CAASTRO PhD candidate Tristan Reynolds and Evolving Theme leader Professor Lister Staveley-Smith, both at ICRAR’s University of Western Australia node, led a series of commissioning tests of the CSIRO-designed technology.

Radio telescope feeds are traditionally shaped like horns, and ‘see’ only one pixel of sky at a time. Phased-array feeds are arrays of simple receptors, closely packed together. They have a wider field of view – that is, they see more of the sky at one time.

The new phased-array feed was built by CSIRO for the 100-m Effelsberg telescope in Germany, owned and operated by the Max Planck Institute for Radio Astronomy. Before it was shipped to Germany, Mr Reynolds, Professor Staveley-Smith and their colleagues tested its capabilities during six months of test observations on CSIRO’s Parkes 64-m telescope.

The results of those tests have now been accepted for publication, and show the technology has great promise.

The feed was able to detect one of the fundamental components of the Universe, atomic hydrogen (HI), at much greater distances than is routinely possible. This suggests it may be useful for a new technique, HI intensity mapping, which radio astronomers are just starting to explore.

Using this technique, a radio telescope can capture the aggregate hydrogen emission signal over relatively large patches of sky (tens of millions of light years), in thin ‘slices’ of redshift (distance). This produces an image with fairly coarse 3D pixels. In turn, such images can tell us more about how the abundance and distribution of hydrogen have changed over time.

The Parkes commissioning tests also showed that the phased-array feed helps counter the impact of radio interference – unwanted radio signals arising from human activities. And as a bonus, it nearly eliminated an unwanted signal pattern (caused by radio waves reflecting off parts of the telescope) that has made it hard to calibrate the telescope.

Professor Staveley-Smith is leading a bid to fund the development of another phased-array feed to be used permanently on Parkes. This one would be cryogenically cooled to improve its performance. Such a cooled feed could be used for many kinds of science, including looking the signature of an exotic form of matter (positronium – an electron plus its antiparticle, a positron) in the centre of our Galaxy.

Publication

Tristan Reynolds, Lister Staveley-Smith, Jonghwan Rhee, Tobias Westmeier, Aaron Chippendale, Xinping Deng, Ron Ekers and Michael Kramer, “Spectral-line Observations Using a Phased Array Feed on the Parkes Telescope”.
Accepted for publication in Publications of the Astronomical Society of Australia. Available on arXiv: https://arxiv.org/abs/1709.05085

The ARC Centre of Excellence for All-sky Astrophysics (CAASTRO) is a collaboration between The University of Sydney, The Australian National University, The University of Melbourne, Swinburne University of Technology, The University of Queensland, The University of Western Australia and Curtin University, the last two participating together as the International Centre for Radio Astronomy Research (ICRAR). CAASTRO is funded under the Australian Research Council (ARC) Centre of Excellence program, with additional funding from the seven participating universities and from the NSW State Government’s Science Leveraging Fund.

Contacts

 Professor Lister Staveley-Smith (ICRAR/University of Western Australia)
Ph: +61 8 6488 4550        E: Lister.Staveley-Smith@uwa.edu.au

Tristan Reynolds (ICRAR/University of Western Australia)
Ph: +61 403 540 020        E: Tristan.Reynolds@research.uwa.edu.au

Helen Sim (CAASTRO)
Ph: +61 419 635 905        E: Helen.Sim@sydney.edu.au