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Distant "Super-Starburst" Galaxies Hide Active Black Holes
Birmingham, UK (SPX) Apr 05, 2005 A team of European scientists has used Virtual Observatories to compare observations of distant "starburst" galaxies made at radio and X-ray wavelengths. This is the first study to combine the highest resolution and sensitivity radio and X-ray images which penetrate the dust hiding the centres of some of these distant galaxies. The team focused on galaxies so far away that their radiation took more than six billion years to reach us. The galaxies are seen as they were when they were less than half the age that the Universe is today. Speaking on Tuesday 5 April at the RAS National Astronomy Meeting in Birmingham, Dr. Anita Richards (Jodrell Bank Observatory, University of Manchester) will explain how the team used the UK's MERLIN array of radio telescopes and the Very Large Array to investigate how galaxies in the early Universe differ from those nearby. "The more remote starburst galaxies, so called because of their high rate of star formation, typically produce 1,000 or more solar masses of stars per year - at least 50 times more than the most active star-forming galaxies in the nearby Universe," said Dr. Richards. "Each distant starburst region is tens of thousands of light years across, equivalent to about the inner quarter of the Milky Way - also vastly larger than any such regions found in our part of the Universe." The radio search took place in an area known as the Hubble Space Telescope Deep Field North - a patch of sky smaller than the full Moon that contains tens of thousands of galaxies. Apart from Hubble, radio telescope arrays are the only instruments that can see detailed structures within these galaxies. Moreover, only radio or X-ray emissions can penetrate the dense dust in the innermost regions of some of these galaxies. The two main sources of radio waves and X-rays are star formation and emissions from Active Galactic Nuclei (AGN) that are generated when material is sucked into a massive black hole and ejected in jets. The team found about twice as many starbursts as AGN, where these could be distinguished in radio images. The UK AstroGrid and the European AVO - parts of the international Virtual Observatory - were used to find counterparts for the radio sources from a variety of other data held by archives and observatories around the world. In this way it was discovered that 50 distant X-ray sources with measured redshifts had also been detected by the Chandra space observatory. Virtual Observatory tools made it easy to calculate the intrinsic brightness of the sources, corrected for distance and redshift. However, the team found that there was no obvious relationship between radio and X-ray luminosity. This was a surprise since there is such a link in most local starburst galaxies.
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