South Africa’s Karoo-based KAT-7 radio telescope array (also known as the MeerKAT Precursor Array) has made a major step in its transition from being an engineering prototype to an operational and scientifically useful instrument. The seven-dish array has successfully observed radio emissions from neutral hydrogen gas in the NGC 3109 galaxy, which is located some 4.3-million light years from earth.
“These exciting results achieved by KAT-7 have given us confidence that we know how to build a cutting-edge radio telescope in Africa to answer some of the fundamental questions in radio astronomy,” enthuses SKA South Africa director Dr Bernie Fanaroff. “Our team in the SKA South Africa project and universities has again shown that they can deliver cutting-edge technology and do excellent science on a very tight schedule.”
Neutral hydrogen gas radio emissions have an exact frequency of 1 420 MHz. Those from NGC 3109 were processed in KAT-7’s correlator, which currently can determine the velocity of the gas to an accuracy of 10 km/s, but, by the end of this year, will have been upgraded to achieve an accuracy of 1 km/s.
“Such a high velocity resolution will allow us to distinguish between the conventional models [of the universe] which suppose the presence of an important quantity of dark matter (matter that cannot be seen but that is detected by its gravitational influence) and the Modified Newtonian Dynamics ([commonly called] Mond) models which suppose that no dark matter is present but that it is instead the laws of gravity that change on galaxy scales,” says University of Cape Town South African SKA Research Chair (Multi Wavelength Astronomy) professor Claude Carignan.
NGC 3109 is notable for a significant warp in its disk. “We also speculate that . . . [the] unusual warp in the disk of this galaxy could be caused by a tidal interaction with its dwarf companion galaxy known as Antlia,” suggests Carignan. “Future KAT-7 observations should reveal more information on this possible interaction.” Interestingly, NGC was discovered by British astronomer John Herschel in 1835 while he was carrying out astronomical observations in South Africa.
KAT-7 was originally a prototype for the MeerKAT radio telescope array, now being developed at the same location in the Karoo. MeerKAT will comprise 64 dishes, each with a diameter of 13.5 m, and is itself intended as a precursor to the giant international Square Kilometre Array (SKA) radio telescope. South Africa and Australia are the two countries competing to host the SKA (although there has been talk of splitting it between the two countries). The decision should be announced in the near future. Should South Africa win, MeerKAT would become part of the SKA. Should Australia win, MeerKAT would remain a major, and globally important, scientific instrument.
“A large proportion of the science planned for the SKA – and MeerKAT – involves [the] mapping of the universe using neutral hydrogen,” explains Fanaroff. “Because of the ongoing expansion of the universe, distant galaxies are moving away from us. Measuring the frequency of the spectral line from neutral hydrogen in those galaxies allows us to work out how far away they are. By finding billions of distant galaxies, astronomers will be able to map the structure of the universe and how it has changed over time. This cosmic census of the neutral hydrogen in galaxies – far and near – is essential in understanding the deeper physics of the universe, by answering fundamental questions such as the nature of dark matter and dark energy.”
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Article source: http://www.engineeringnews.co.za/article/karoo-radio-telescope-reaches-another-milestone-2012-03-30