Sky Survey Provides New Radio "View" of Universe


10/21/2004 - 37-04r
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Astronomers using the National Science Foundation's Very Large Array (VLA) have overcome longstanding technical hurdles to map the sky at little-explored radio frequencies that may provide a tantalizing look deep into the early Universe. The scientists have released images and data covering half of the sky visible from the VLA, and hope to complete their survey by the end of next year. The VLA Low-frequency Sky Survey (VLSS) is producing sky images made at an observing frequency of 74 MHz, a far lower frequency than used for most current radio-astronomy research. The team of astronomers represent the Naval Research Laboratory, the National Radio Astronomy Observatory, the National Research Council, and the University of Maryland.

"Because of the Earth's ionosphere, such a low frequency has proven very difficult for high-quality imaging, and it is only in the past few years that we have developed the techniques that make a project like the VLSS possible," said Dr. Rick Perley, of the National Radio Astronomy Observatory (NRAO) in Socorro, NM. Because the high-quality VLSS images will give astronomers a look at the Universe through what essentially is a new "window," they expect the images to reveal some rare and important objects.

"We expect to find very distant radio galaxies - galaxies spewing jets of material at nearly light speed and powered by supermassive black holes," said Dr. Joseph Lazio of the Naval Research Laboratory in Washington, DC. "By determining just how distant these radio galaxies are, we will learn how early the black holes formed in the history of the Universe," he added.

Another tantalizing possibility is that the low-frequency images may reveal "halos" and "relics" produced by collisions of galaxies in clusters. If the halos and relics are found in the distant, and thus early, Universe, it will give scientists important clues about the timetable for formation of large-scale structure. In addition, the astronomers hope that the VLSS images may show previously-undiscovered pulsars - superdense, spinning neutron stars. Massive planets - "super Jupiters" circling stars beyond the Sun - also might reveal themselves through bursts of radio emission at the frequency of this survey, the astronomers speculated.

Images from the survey are being made available to other scientists as soon as they are completed. When completed, the survey will have used nearly 800 hours of VLA observing time. The newly-released images and data are available via the NRAO Web site. "By doing this survey and making the results available, we are bringing low-frequency radio data, previously quite difficult to produce, to all astronomers in a simple and easy manner," Perley said. "We also expect that this survey will spur additional research into objects that scientists find puzzling or interesting," Perley said. "We really will have to wait for years to know the full scientific benefit of this survey," he said.

In addition to Drs. Perley and Lazio, the VLSS team includes Dr. James Condon and Dr. William Cotton of NRAO; Dr. Namir Kassim of the Naval Research Laboratory; Dr. Aaron Cohen and Dr. Wendy Lane of the National Research Council and the Naval Research Laboratory; and Dr. William Erickson of the University of Maryland.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement with Associated Universities, Inc.

More information on NRL's involvement with VLSS can be found on the web site: http://lwa.nrl.navy.mil/VLSS.




This false color image shows a small portion of the radio sky as seen by the VLA in the VLSS. White regions indicate radio-bright emitting galaxies, while deep red/black indicate regions of little or no radio emission. All of the "spots" in the image are radio-bright galaxies. The extended object in the lower right is a nearby radio galaxy. Its elongated shape results from jets of highly relativistic material being shot in opposing directions from the environment of a supermassive black hole located near the center of the source. (The supermassive black hole and its environment are not visible in this image.) The typical radio-bright galaxy in this image is only about half-way across the observable Universe, but astronomers are trying to determine if there might be an extremely distant one among the more typical ones.
A "rogues' gallery" of radio galaxy types seen in the VLSS. White regions indicate radio-bright emitting regions in the galaxies, while deep red/black indicate regions of little or no radio emission. In all cases, the radio galaxies are thought to shine because of jets of highly relativistic material being shot from the environment of a supermassive black hole in the center of the radio galaxy. The diversity of shapes probably reflects the environment of the radio galaxy itself as well as the history of the supermassive black hole and how much material has fallen into it.




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