Scientists of Sloan Digital Sky Survey Discover Most Distant QuasarBatavia, Ill.-- Scientists of the Sloan Digital Sky Survey have announced the discovery of the most distant quasar ever observed.
At a December 4 collaboration meeting at the Department of Energy's Fermi National Accelerator Laboratory near Chicago, Princeton University graduate student Xiaohui Fan broke the news. Using data from only the first months of the initial shakedown operation of new sky-mapping technology, Fan said, the Sky Survey had already discovered three of the four most distant quasars currently known.
"We could identify these quasars so readily," Fan said, "because of the Sky Survey's unique characteristics: its superb telescope and camera, the power of the analysis software, and the large amount of sky it can cover."
Sky Survey astronomer Michael Strauss of Princeton University, Fan's faculty advisor, described the discovery of the most distant of all quasars -- compact yet luminous objects thought to be powered by super-massive black holes.
"Xiaohui and I were in the basement of Peyton Hall at Princeton, operating the 3.5-meter diameter telescope at Apache Point Observatory over the Internet to follow up on quasar candidates from the Sky Survey data. It was 1:30 a.m. on Thanksgiving morning, and we only had about half an hour of observing time left. Xiaohui suggested observing one of our last promising high-redshift quasar candidates before we finished up. As soon as we saw the spectrum, we knew we had a record-breaking quasar."
Secretary of Energy Bill Richardson congratulated the Sky Survey astronomers on their discovery.
"You are extending the frontiers of human understanding into new and uncharted territory," Secretary Richardson said. "I am proud that the Department of Energy supports science that spans the entire panorama of our universe, from the inner recesses of the proton to the outermost reaches of space."
Remarkably, the Sky Survey telescope at Apache Point Observatory in southern New Mexico unveiled the three quasars during an early stage of its commissioning, after examining just a narrow slice of the sky, the first 1 percent of its planned sky coverage. Only a portion of that data has so far been analyzed. Members of the team were still calibrating instruments, building data archives, and installing a new monitor telescope when the discovery data were taken in September, just months after first light.
"The National Science Foundation is gratified to see the promise of the Sloan Digital Sky Survey being realized, even in these early results," said Hugh Van Horn, director of NSF's Division of Astronomical Sciences. "We are eager to see the resulting data archive become publicly available to all qualified U.S. astronomers, and we are working with the project to help expedite this release."
More than 80 scientists meeting at Fermilab, near Chicago, received the news enthusiastically, cheering a series of color images and spectral plots that revealed the new record-holders, quasars with redshifts of 5.0, 4.9, and 4.75. Redshift is the amount by which light is shifted toward the red end of an object's spectrum by the expansion of the universe. Astronomers use redshift as a measure of the distance of celestial objects: the higher the redshift, the greater the distance and the younger the universe when the light was emitted. The newly discovered quasars mark an epoch when the universe was less than a billion years old and a sixth of its current size.
The most distant quasar now surpasses a quasar discovered in 1991 at a redshift of 4.89 by astronomers Donald Schneider, Maarten Schmidt and James Gunn. Two of the three, Gunn and Schneider, were at the Fermilab meeting Friday morning, applauding with their colleagues at the announcement of the news.
"The results are revolutionary," Schneider, a Sky Survey collaborating astronomer from Pennsylvania State University, said afterward. "What we have found is not totally unexpected but it is extraordinary at this early stage. Looking at only 1 percent of the data and using prototype software and only a preliminary calibration to evaluate it, we have achieved a 70 percent success rate in identifying bright high-redshift quasars. At the current rate of discovery, by the end of the Survey we should find more than 500 quasars with redshift greater than 4.75."
Many said long-held expectations were already being confirmed that the project will readily generate masses of detailed data that will not only chart the skies, but also present a magnificent panorama of the large-scale structure of the universe. Imaging the slender slice of sky, the Sky Survey's new wide-field telescope electronically recorded millions of objects during its trial runs. The images depicted a broad range of objects--from nearby asteroids between Mars and Jupiter to mysterious hybrid galaxies--and left scientists with an astonishing array of data to analyze.
For weeks, Fan and Fermilab scientists Heidi Newberg and Brian Yanny sifted through the huge database, relying on the Sky Survey's new filtering techniques to select a few dozen objects they suspected might be high-redshift quasars. Fan and Strauss then used a separate 3.5-meter telescope at Apache Point Observatory to verify that they had detected 12 new quasars at redshifts above 3.6. This represented an extraordinary success rate for the infant project, barely beyond its preliminary stages of testing.
"We had planned all along for this discovery. Nevertheless, we were really excited when we actually found high-redshift quasars," said Alex Szalay, (pictured at right) professor of astrophysics at The Johns Hopkins University and a member of the team for almost a decade. "The real challenge for us now will be recognizing objects whose existence we are not even aware of. We'll need to develop new software tools to mine the data."
Alan Bunner, science program director for the Structure and Evolution of the Universe for the National Aeronautics and Space Administration, added that "NASA is pleased to be a part of this pioneering project that will greatly enhance both ground- and space-based astronomy for the next 50 years."
The ultimate goal of the Sky Survey, an international collaboration of more than 100 scientists and engineers, is to map one quarter of the sky and create a systematic, three-dimensional picture of the universe 100 times larger than in previous surveys. The Survey team will first create a digital image of the sky in five colors, using the most complex astronomical camera ever built, mounted on a 2.5 meter telescope built for the survey. From the digital images, astronomers will choose the million brightest galaxies and use a specially designed spectrograph to measure the redshifts of the million brightest galaxies, 600 at a time. The redshifts will allow scientists to determine the distances to these million galaxies, adding the third dimension. The Survey will also find redshifts for 100,000 quasars.
"Quasars are a major target of the Sky Survey," said Sadanori Okamura, a University of Tokyo astronomer. "With the luminosity of more than 100 galaxies emitted from a volume no larger than our solar system, quasars continue to mystify astronomers. Quasars may well play a significant role in the evolution of structures in the universe."
Astronomers don't actually know how quasars fit into the scheme of things, said astronomer Richard Kron of the University of Chicago and Fermilab.
"We have reason to believe," Kron said, "that they are powered by massive black holes whose energy comes from intensely hot material that's rapidly funneling into the hole. But we don't understand where the holes came from."
University of Washington astronomer Craig Hogan underscored the significance of quasars.
"As the most powerful beacons in the sky," said Hogan, "rare, bright quasars give astronomers an excellent way to examine intervening material that absorbs their light. Ironically, the brightest things in the universe provide probes for even the emptiest parts of intergalactic space."
>From the beginning, scientists had planned to use the neighboring 3.5-meter telescope at Apache Point Observatory to investigate interesting objects culled from the huge lists generated each night by the smaller Sky Survey telescope.
"The ability to follow up quickly on quasar candidates with the 3.5-meter telescope has made this discovery possible," said University of Chicago astronomer Don York, first director of the Sky Survey and of the Apache Point Observatory. "It has proven the vision that many of us had for the synergy between the two telescopes."
Data from Sky Survey commissioning runs in June and September were processed through data analysis "pipelines" at Fermilab.
"The software pipelines automatically detect celestial objects," said Princeton scientist Robert Lupton. "For each one, they measure the intensity of five colors of light passing through the camera. Astronomers can then separate stars from quasars by their distinctive colors."
At Friday's meeting in Chicago, standing before a distinguished gathering of senior astronomers, Fan presented the data with a sense of their momentous foreshadowing. "There is every reason to believe," the Princeton student said, "that in years to come there will be even more exciting results from this survey. We have found the most distant quasars quite easily, after people have been searching for them for decades. We can look forward to many years of good science."
Participating institutions in the Sloan Digital Sky Survey include The University of Chicago, Fermilab, the Institute for Advanced Study, the Japanese Participation Group, The Johns Hopkins University, Princeton University, the United States Naval Observatory and the University of Washington. Apache Point Observatory, site of the Sloan Digital Sky Survey, is owned by the Astrophysical Research Consortium, a nonprofit corporation consisting of seven research institutions, and is operated by New Mexico State University. Funding to date for the project has been provided by the Alfred P. Sloan Foundation, Sky Survey member institutions, the National Science Foundation, the National Aeronautics and Space Administration and the U.S. Department of Energy.
News release and high-resolution photos available at http://www.sdss.org/news/releases/19981208.qso.html
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