Small cosmic ‘fish’ points to big haul for SKA Pathfinder
A wisp of cosmic radio waves, emitted before our solar system was born, shows that a new radio telescope will be able to detect galaxies other telescopes can’t. The work, led by Dr James Allison of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia, was announced today (6 July) at the National Astronomy Meeting in Llandudno, north Wales.
Australian Square Kilometre Array Pathfinder (ASKAP), a new radio telescope 300 kilometres inland from the Western Australian town of Geraldton.The finding was one of the first made with CSIRO’s
The discovery team, which included astronomers from the University of Sydney and the Australian Research Council’s Centre of Excellence for All-sky Astrophysics (CAASTRO), worked with just six of ASKAP’s 36 radio dishes, a subset being used to commission the telescope.
Coming from the galaxy PKS B1740-517 in the direction of the southern constellation of Ara, the radio signal had travelled through space for five billion years before being captured.
It carries the ‘imprint’ of cold hydrogen gas that it passed through on its way here. Cold hydrogen gas is the raw material for forming stars and is plentiful in most galaxies. Astronomers can spot a galaxy from its hydrogen gas even when its starlight is faint or hidden by dust. The newly found signal is small but has big implications. “This catch shows we’re going to bag a big haul of galaxies,” said Dr Allison.
Although tiny, the signal stood out clearly in the ASKAP data. Many radio telescopes are bedevilled by ‘radio interference’—unwanted signals that clutter up the spectrum. “That makes looking for this kind of signal like hunting for a small fish in a bed of seaweed,” Dr Allison said. But ASKAP’s site is exceptionally ‘radio quiet’. “Here we look through clear water to find the fish.”
ASKAP also gives astronomers a very large ‘net’ with which to trawl for signals—a chunk of radio spectrum to search through that’s 300 MHz wide. “That’s more than most telescopes have, and it gives us a better chance of finding something new,” Dr Allison said.
Professor Elaine Sadler, Professor of Astrophysics at the University of Sydney and Director of the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), was a member of the research team for this project. She leads a large ASKAP survey, now in the planning stage, that’s aimed at detecting several hundred galaxies.
“ASKAP looks at a relatively unexplored part of the radio spectrum, 700 to 1800 megahertz,” she said. “This means we’ll be able to detect hydrogen gas deeper in space and, thanks to ASKAP’s wide field of view, also over a much larger volume than we could before. We’ll be hunting for galaxies that are five to eight billion years old, a timespan that represents a fifth of the Universe’s history.”
Ten billion years ago, galaxies were making stars ten times faster than they do today. By studying galaxies five to eight billion years old, astronomers hope to understand why the rate dropped.
“We want to learn how much hydrogen galaxies had in this period for forming stars,” Professor Sadler said. “Until now we’ve had few tools for doing that.”
Professor Sadler’s new survey is called ‘FLASH’, which stands for ‘the first large absorption survey in HI’ (HI being cold atomic hydrogen gas). A pilot survey for FLASH will begin on ASKAP next year.
Images, animation and captions
Animation showing a radio signal travelling from a distant source to our Milky Way, and being absorbed along the way by an intervening gas cloud. Credit: CAASTRO and Swinburne Astronomy Productions
An optical image of the radio galaxy PKS B1740-517, made with the Gemini South telescope. The galaxy is indicated by the green tick marks, which show the location of the slit used to obtain a spectrum of this object. This galaxy has a black hole at its centre: jets flowing away from that create the strong radio source detected with ASKAP. Credit: M. Whiting (CSIRO) from Gemini South data
The same image but with the tick marks removed. Credit: M. Whiting (CSIRO) from Gemini South data
CSIRO's Australian SKA Pathfinder telescope. Credit: CSIRO
Astronomer Dr James Allison. Credit: CSIRO
Ms Helen Sim
Notes for editors
The Square Kilometre Array (SKA) project is an international effort to build the world’s largest radio telescope, led by the SKA Organisation. The SKA will conduct transformational science to improve our understanding of the Universe and the laws of fundamental physics, monitoring the sky in unprecedented detail and mapping it hundreds of times faster than any current facility.
The SKA is not a single telescope, but a collection of telescopes or instruments, called an array, to be spread over long distances. The SKA is to be constructed in two phases: Phase 1 (called SKA1) in South Africa and Australia; Phase 2 (called SKA2) expanding into other African countries, with the component in Australia also being expanded.
Already supported by 10 member countries – Australia, Canada, China, India, Italy, New Zealand, South Africa, Sweden, The Netherlands and the United Kingdom – the SKA Organisation has brought together some of the world’s finest scientists, engineers and policy makers and more than 100 companies and research institutions across 20 countries in the design and development of the telescope. Construction of the SKA is set to start in 2018, with early science observations in 2020.
ASKAP is one of the precursor telescopes to the SKA telescope. Other precursors are the Murchison Widefield Array in Australia, and the South African MeerKAT telescope.
The Royal Astronomical Society National Astronomy Meeting (NAM 2015) will take place in Llandudno, Wales, from 5-9 July. NAM 2015 will be held in conjunction with the annual meetings of the UK Solar Physics (UKSP) and Magnetosphere Ionosphere Solar-Terrestrial physics (MIST) groups. The conference is principally sponsored by the Royal Astronomical Society (RAS) and the Science and Technology Facilities Council (STFC). Follow the conference on Twitter
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