Three Distant Quasars Found at Edge of the Universe

SEATTLE — Astronomers with the Sloan Digital Sky Survey have discovered three of the oldest, most distant quasars yet found — quasars close to the Big Bang that began the universe.

Xiaohui Fan of the University of Arizona’s Steward Observatory in Tucson, Ariz., will present the results today (9 Jan. 2003) at the American Astronomical Society’s meeting in Seattle.

Fan, leader of the team that discovered the objects, explained that these distant quasars — compact but luminous objects thought to be powered by super-massive black holes — reach back to a time when the universe was just 800 million years old. Fan said the highest redshift quasar is roughly 13 billion light years away and was discovered recently in the constellation Ursa Major.

“The Sloan Digital Sky Survey discoveries of quasars at high redshift are coming at a time that astronomers are discovering normal galaxies at similarly high redshift,” said astronomer Michael Strauss of Princeton University. “These discoveries are giving us the first glimpse of the universe when it was only 5 percent of its present age.”

(When a celestial object moves away from Earth, the lines in its spectrum shift toward longer, red wavelengths. This so-called redshift is proportional to the object’s velocity. Astronomers now believe that the most distant objects recede from Earth at the highest velocities, so the farther away an object is, the greater its redshift.)

The discovery of the quasars required the efforts of a number of scientists working with different telescopes. The key observation was made by the Sloan Digital Sky Survey’s 2.5-meter telescope at Apache Point Observatory in New Mexico, which first identified the objects as possible distant quasars.

“Finding the rare, high-redshift quasars is a needle in a haystack operation made worse by the fact that a lot of the straw looks like needles at first glance,” Fan said. “That means that there are a lot of stars which look like high-redshift quasar candidates.”

Fan and Strauss obtained infrared images of the most likely candidates with Apache Point’s 3.5-meter telescope and obtained spectroscopic measurements to properly identify these objects and determine their redshift measurements.

“These objects are quite faint and, although the initial spectra suggested we’d found three distant quasars, we needed observations on large telescopes to be certain of our interpretations,” Strauss added.

“Verification with larger telescopes is crucial,” explained Eva Grebel, a Sloan Survey collaborator and staff astronomer at the Max-Planck Institute for Astronomy in Heidelberg. “They allow us to obtain targeted spectroscopic follow-up of the faint objects that are identified as candidates photometrically by the Sloan Digital Sky Survey. With spectra, we can distinguish distant quasar candidates powered by black holes with a billion times the sun’s mass from tiny nearby stars with only a fraction of the mass of the sun.”

During the past year, members of the Sloan Digital Sky Survey team obtained further spectra of the quasars with the 10-meter (400 inch) Keck Observatory in Hawaii, the 9.2-meter (368 inch) Hobby-Eberly telescope in west Texas and the 3.5-meter (158 inch) Calar Alto Observatory telescope in southern Spain.

“The spectra show unambiguously that the three quasars have redshifts of 6.4, 6.2 and 6.1,” said Don Schneider, a collaborating Sky Survey astronomer at Pennsylvania State University. “Only one quasar had been previously known to have a redshift larger than six.” The previous record-holder, at redshift of 6.28, was discovered in 2001 by the Sloan Digital Sky Survey consortium.

Cosmologist Robert Becker of the University of California-Davis and the Lawrence Livermore National Laboratory, noted that “the Sloan Survey has now discovered the seven most distant known quasars.”

“The Sloan Survey has generated a sample of quasars which stretches through all of cosmic time, from 800 million years after the Big Bang to the present,” said James Gunn of Princeton University, and the project scientist of the Sloan Survey. “These data will be invaluable for the next major effort of the Sloan Survey quasar team, namely to characterize the evolution of quasars from their formation to the present.”

(A complete list of people contributing to the discoveries of new, more distant quasars is posted on the NEWS Section of the Sloan Digital Sky Survey web site at http://www.sdss.org)

ABOUT THE SLOAN DIGITAL SKY SURVEY (SDSS)

The Sloan Digital Sky Survey (sdss.org) will map in detail one-quarter of the entire sky, determining the positions and absolute brightness of 100 million celestial objects. It will also measure the distances to more than a million galaxies and quasars. The Astrophysical Research Consortium (ARC) operates Apache Point Observatory, site of the SDSS telescopes.

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 (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, 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.

CONTACTS: During the AAS Meeting, Xiaohui (pronounced Shiao-wee) Fan and other collaborators can be reached through Gary Ruderman or Richard Kron of the Sloan Digital Sky Survey.

ART:
A picture of the Z 6.4 Quasar can be found at:http://sancerre.as.arizona.edu/~fan/PR/2002/z64.gif
A picture of the Z 6.2 Quasar can be found at: http://sancerre.as.arizona.edu/~fan/PR/2002/z62.gif
A picture of the Z 6.1 Quasar can be found at:http://sancerre.as.arizona.edu/~fan/PR/2002/z61.gif
Spectra for all new Z 6.0 quasars can be found at: http://sancerre.as.arizona.edu/~fan/PR/2002/spectra.gif

CAPTION: The red dots in the different pictures are actually three of the four most distant quasars ever discovered. The 6.4, 6.2 and 6.1 quasars — compact but luminous objects thought to be powered by super-massive black holes — reach back to a time when the universe was just 800 million years old. The objects are roughly 13 billion light years away and were discovered earlier this year by the Sloan Digital Sky Survey (www.sdss.org) in the constellation Ursa Major. CREDIT: Sloan Digital Sky Survey