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Wizard new work from the e-MERLIN telescope array
Posted: 27 March 2012

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A network of radio telescopes, with the mighty 76-metre dish of Jodrell Bank Observatory’s Lovell Telescope at its hub, has begun a pathfinding survey to measure the star-formation history of the Universe, with the first results being presented today at the Royal Astronomical Society’s National Astronomy Meeting at the University of Manchester.

The first images from the e-MERGE survey, showing radio emission tracing star-formation in distant galaxies. The background image is courtesy of the EVLA, whereas the fine detail insets are a product of e-MERLIN observations. Image: N Wrigley/Jodrell Bank Centre for Astrophysics.

e-MERLIN is a revolutionary upgrade to the old MERLIN (Multi-Element Radio-Linked Interferometer Network) network incorporating seven radio telescopes across the UK, including the Lovell Telescope and the Mark II telescope at Jodrell Bank, a 25-metre dish at Darnhall in Cheshire and a 32-metre telescope at Cambridge. The telescopes have now been linked by optical fibres that allow greater resolution and sensitivity and, working with a similar network in the United States – the Expanded Very Large Array or EVLA – radio astronomers have embarked on an ambitious project called e-MERGE (e-MERlin Galaxy Evolution Survey), that seeks to map out the star-formation history of the Universe by making the deepest ever radio map of the area of sky imaged for the famous Hubble Deep Field. The initial images, assembled by Manchester graduate student Nick Wrigley under the supervision of Drs Rob Beswick and Tom Muxlow and revealed at the National Astronomy Meeting, form part of e-MERLIN’s commissioning stage.

The seven dishes in the e-MERLIN network. Image: Jodrell Bank Centre for Astrophysics.

e-MERGE’s remit is grand in scale. “We will image several thousand galaxies, sampling star-forming galaxies out to redshifts greater than 5, although clearly those seen at distances approaching 12 billion light years will be restricted to more luminous types,” says Muxlow. The idea is to track the radio emission at two wavebands of 1400–1700MHz and 4–6 GHz from plasma (ionised, or electrified gas) emanating from supernova explosions, which are the catastrophic destruction of massive stars. Because these massive stars don’t live for very long – a few million years – they are still in or close to their birthplaces, and starbirth is continuing apace around them, hence making them good tracers for star formation at distances of billions of light years. Radio waves are the perfect means by which to study star formation at such large distances because, unlike visible and ultraviolet light, radio waves are not absorbed by intervening dust and gas that reside in these star forming regions.

The Hubble Deep Field, the targeted area of the sky for the e-MERGE survey. The most distant galaxies seen here have a lookback time of 12 billion years. Image: Robert Williams and the Hubble Deep Field Team (STScI) and NASA.

The images show fine detail down to sub-arcsecond resolution, revealing details in the structure of the various features emitting radio waves. Combined with spectral data, this high-resolution images allow radio astronomers to distinguish between emission from star-forming regions and emission from active black holes, further refining the accuracy of the observations. Indeed, it may be that active black holes, which have powerful radiation jets that burst out into their host galaxies, may also play a role in star formation within galaxies. “Do the active black holes and jets trigger star formation or quench it?” asks Muxlow.

The new images show bright galaxies at distances for seven billion light years. When the e-MERGE survey is complete, it will provide information on star-formation in galaxies up to lookback times of 12 billion years, complementing Hubble’s visible light observations of the same galaxies in the Hubble Deep Field.

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