Summer 2000 -- Vol. 17, No. 1

International Team of Astronomers Finds Most Distant Object

In April 2000 an international team of astronomers, including Penn State professor of astronomy and
astrophysics Donald Schneider, announced it had discovered the most distant known object in the universe. 
The object was first spotted in March while the scientists were examining data from the Sloan Digital Sky
Survey (SDSS), a project designed to map a large portion of the sky in unprecedented detail.

Xioahui Fan, a Princeton graduate student, was examining some of the SDSS data base and noted the presence of a faint, red object that had a very unusual color.  A spectrum of the source was obtained on 29 March with the Keck telescope in Hawaii and within minutes the astronomers knew the radiation they had just recorded had originated in a distant quasar when the universe was less than a billion years old.  Quasars are thought to be massive (up to a billion times the mass of the Sun) black holes that are accreting matter at the rate of more than one solar mass per year.

 

Donald Schneider's Record of Discovering the Most Distant Quasar Date Redshift* Schneider's Collaborators Most Distant Object? 1987 1989 1991 1998 1999 2000 4.04 4.73 4.90 5.00 5.02 5.82 Maarten Schmidt+James Gunn Maarten Schmidt+James Gunn Maarten Schmidt+James Gunn Sloan Digital Sky Survey Team Sloan Digital Sky Survey Team Sloan Digital Sky Survey Team Yes Yes Yes No No Yes *The distance to a quasar is typically expressed in terms of the object¹s redshift, which is a measure of how far the wavelength of its light is lengthened, or shifted to the red end of the spectrum. The larger the redshift, the more distant the source (see box, page 16). The quasar Schneider and his collaborators discovered in March 2000 has a redshift of 5.82, breaking the distance record previously held by a galaxy with redshift 5.7 discovered last year by Esther Hu and colleagues at the University of Hawaii and the Institute of Astronomy in Cambridge, England.

Distances to quasars are usually expressed in terms of the object's redshift, which is a measure of how far the
wavelength of its light is lengthened, or shifted, to the red end of the spectrum; the larger the redshift, the more
distant the source.  The newly discovered quasar has a redshift of 5.82, breaking the distance record previously held by a galaxy with redshift of 5.7, discovered last year by Esther Hu and colleagues at the University of Hawaii and the Institute of Astronomy in Cambridge, England.  Moreover--and ultimately perhaps much more significant --this isn't the first far-off quasar the SDSS sky survey has found.

"Finding the most distant object is, of course, an event worth noting, but what particularly excites me is the un-precedented rate at which the SDSS is finding high-redshift quasars," said Schneider.  "When the SDSS obtained its first observations in May 1998, only one quasar was known with a redshift larger than 4.74, and that was a redshift 4.90 quasar discovered back in 1991. As of the middle of April 2000, the SDSS has found a total of 12 such objects; five with redshifts above five."

This theme was echoed by the SDSS Project Scientist, James Gunn of Princeton University.

"The real significance of the Sloan quasars," said Gunn,"is not their record-breaking distances but the size and quality of the sample.  The scale and the homogeneity of the data will allow SDSS and other scientists to use quasars to chart the birth and formation of galaxies, explore structure on the largest scales, and better understand black holes.  Past quasar surveys have included a smaller and less uniform selection of objects."

Schneider is the chairman of the SDSS Quasar Science Working Group, and is using the Hobby-Eberly Telescope at McDonald Observatory to observe SDSS high-redshift quasar candidates. Penn State is the originator and one of the principal operating partners of the Hobby-Eberly Telescope, the largest optical telescope on the North American continent and one of the largest in the world.  To date, the Hobby-Eberly Telescope has discovered more than two dozen high-redshift quasars, and Schneider believes that the best is yet to come.  "The SDSS has only covered a few percent of the planned survey area, and the Hobby-Eberly Telescope has only recently completed its commissioning phase.  I will be quite disappointed if in five years we have not discovered more than 100 quasars above redshift five."

Penn State

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