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

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.

“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 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 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. The survey will use
some 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 saidd. “We really will have to wait for years to know
the full scientific benefit of this survey,” he said.

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

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

NOTE: This release, with graphics, may be found on
the NRAO Web site, at: http://www.nrao.edu/pr/2004/vlss/