Summer 2004 -- Vol. 21

Three of the Most Distant Quasars Found at Edge of the Universe

	Sloan Digital Sky Survey The Sloan Digital Sky Survey (SDSS) will map in detail one-quarter of the entire sky, determining the positions and absolute brightness of 100 million celestial objects. It also will measure the distances to more than a million galaxies and quasars. The Astrophysical Research Consortium (ARC) operates Apache Point Observatory, site of the Sloan Digital Sky Survey telescopes. The SDSS is a joint project of the University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, the Johns Hopkins University, the Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy, the Max-Planck-Institute for Astrophysics, New Mexico State University, the University of Pittsburgh, Princeton University, the United States Naval Observatory, and the University of Washington. Funding for the project has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Aeronautics and Space Administration, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho, and the Max Planck Society. (http://www.sdss.org)

An international team of scientists from the Sloan Digital Sky Survey, including two astronomers from Penn State, have discovered three of the most distant quasars, including the most distant quasar known. The discoveries, described in a paper published in The Astronomical Journal, relied on observations by one of the world’s largest optical telescopes—the 9.2-meter Hobby-Eberly Telescope—which is partially owned and operated by Penn State.

Donald Schneider, professor of astronomy and astrophysics at Penn State and chairman of the Sloan Survey’s Quasar Science Working Group, noted the key role played by the Hobby-Eberly Telescope in the discovery of the first, third, and fourth most distant quasars. “The Hobby-Eberly Telescope staff deserve a great deal of credit for obtaining these challenging observations,” he said.

The astronomers report that the three quasars are hundreds of times more luminous than our galaxy, and are probably powered by black holes that are more than a billion times the mass of the Sun. The radiation recorded from the quasars last year left the objects when the universe was just 800 million years old. “We are perhaps witnessing the formation of the first large structures in the universe,” said Niel Brandt, professor of astronomy and astrophysics at Penn State, who is also an author on the paper and the leader of the Sloan Survey’s investigation of the X-ray properties of distant quasars. “These objects may provide crucial insights into how nature manages to create large black holes and galaxies.”

The discovery of the quasars required the efforts of many scientists working with different telescopes, including the Hobby-Eberly Telescope. Observations by the Sloan Digital Sky Survey’s 2.5-meter telescope at Apache Point Observatory in New Mexico first identified the objects as possible distant quasars. The candidates were so faint—emitting essentially no visible light—that only near-infrared detectors could detect the objects.

Xiaohui Fan of Steward Observatory and Michael Strauss of Princeton University carried out initial observations of the quasar candidates with Apache Point’s 3.5-meter telescope, but the objects were too faint for this instrument to unambiguously determine their redshifts. Larger telescopes, such as the 9.2-meter Hobby-Eberly and 10-meter Keck telescopes, were used to obtain high-quality data on the quasar candidates.

The distances to all three quasars were measured with data obtained with the Hobby-Eberly Telescope’s Marcario Low-Resolution Spectrograph, which was designed and built by a team led by Gary Hill of the University of Texas. “The queue-scheduled nature of the Hobby-Eberly Telescope allowed it to acquire the data almost as soon as the candidate quasars were identified,” said Larry Ramsey, professor and head of the Department of Astronomy and Astrophysics at Penn State and Project Scientist for the Hobby-Eberly Telescope. “It is clear that the Sloan Survey and the Hobby-Eberly Telescope are a powerful combination for scientific discovery.”

	At left is a low-resolution spectrograph image of the most distant known quasar ever discovered. The redshift 6.4 quasar is seen at a time when the universe was just 800 million years old. The light-travel time from this object to us is about 13 billion years. Also shown: the redshift 6.2 quasar (center) and the redshift 6.1 quasar (right). Credit: Sloan Digital Sky Survey

Schneider notes that the three quasars were found when the Sloan survey had covered only about a third of its planned area. “In the next few years we hope to find more than a dozen of these beacons from the universe’s infancy,” he says. This work marks the eighth time that Schneider has discovered the most-distant quasar.

“The Sloan survey has generated a sample of quasars that stretches through almost all of cosmic time, from 800 million years after the Big Bang to the present,” explained James Gunn of Princeton University, who is the Project Scientist of the Sloan Digital Sky Survey. “These data will be invaluable for the next major effort of the survey’s quasar team, namely to characterize the evolution of quasars from their formation to the present.”

The Marcario Low-Resolution Spectrograph was constructed by the University of Texas at Austin, Stanford University, Ludwig-Maxmilians-Universitat München, the Instituto de Astronomica de la Universidad de Mexico, Georg-August-Universit¨at Göttingen, and Penn State. The instrument is named for Mike Marcario of High Lonesome Optics, who fabricated several optical elements for the spectrograph but died before its completion.

Donald Schneider and Barbara K. Kennedy

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