A New Search for Dark Energy Begins

One of the "first light" spectra taken by the Baryon Oscillation Spectroscopic Survey (BOSS). The top panel shows the targeted blue quasar, highlighted in the image of the sky, which are thought to be supermassive black holes in distant galaxies. At the bottom is shown the BOSS spectrum of the object which allows astronomers to measure the "redshift," or distance to this object. BOSS plans to collect millions of such spectra and use their distances to map the geometry of the Universe. Figure credit: D. Hogg, V. Bhardwaj and N. Ross

The most ambitious attempt yet to trace the history of the universe has seen "first light." The Baryon Oscillation Spectroscopic Survey (BOSS), a part of the Sloan Digital Sky Survey III (SDSS-III), took its first astronomical data on the night of September 14-15 after years of preparations.

That night, astronomers used the Sloan Foundation 2.5-meter telescope at Apache Point Observatory in New Mexico to measure the spectra of a thousand galaxies and quasars, thus starting a quest to eventually collect spectra for 1.4 million galaxies and 160,000 quasars by 2014.

"The data from BOSS will be the best ever obtained on the large- scale structure of the universe," said David Schlegel of the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), the Principal Investigator of BOSS. BOSS uses the same telescope as the original Sloan Digital Sky Survey, but equipped with new, specially-built spectrographs to measure the spectra.

"The new spectrographs are much more efficient in infrared light," explained Natalie Roe of Berkeley Lab, the Instrument Scientist for BOSS. "The light emitted by distant galaxies arrives at Earth as infrared light, so these improved spectrographs are able to look much farther back in time."

The ability to look further back in time is important in allowing BOSS to take advantage of a feature in the universe called "baryon oscillations." Baryon oscillations began when pressure waves traveled through the early universe.

"Like sound waves passing through air, the waves push some of the matter closer together as they travel" said Nikhil Padmanabhan, a BOSS researcher who recently moved from Berkeley Lab to Yale University. "In the early universe, these waves were moving at half the speed of light, but when the universe was only a few hundred thousand years old, the universe cooled enough to halt the waves, leaving a signature 500 million light years in length."

"We can see these frozen waves in the distribution of galaxies today," said Daniel Eisenstein of the University of Arizona, the Director of the SDSS-III. "By measuring the length of the baryon oscillations, we can determine how dark energy has affected the expansion history of the universe. That in turn helps us figure out what dark energy could be."

Photograph of Senior Operations Engineer Dan Long loading the first cartridge of the night into the Sloan Digital Sky Survey telescope. The cartridge holds a "plug-plates" at the top which then holds a thousand optical fibers shown in red and blue. These cartridges are locked into the base of the telescope and are changed many times during a night. Photo credit: D. Long

"Studying baryon oscillations is an exciting method for measuring dark energy in a way that's complementary to techniques in supernova cosmology," said Kyle Dawson of the University of Utah, who is leading the commissioning of BOSS. "BOSS's galaxy measurements will be a revolutionary dataset that will provide rich insights into the Universe," added Martin White of Berkeley Lab, BOSS's survey scientist.

BOSS's first data were taken after many nights of clouds and rain. The first data came from a region of sky in the constellation Aquarius, causing team member Nic Ross to joke that BOSS first light marked the "dawning of the Age of Aquarius" after the famous 60's song by 5th Dimension. Nic has just joined the Berkeley Lab from Pennsylvania State University and notes, "Looks like I'm in for a very hectic, but extremely exciting first month on the job."

The BOSS spectrographs will work with more than two thousand large metal plates that are placed at the focal plane of the telescope; these plates are drilled with the precise locations of nearly two million objects across the northern sky. Optical fibers plugged into a thousand tiny holes in each of these "plug plates" carry the light from each observed galaxy or quasar to BOSS's new spectrographs.

Using these plug plates for the first light image should have been easy, but it didn't quite turn out the way astronomers planned. "In our first test images, it looked like we'd just taken random spectra from all over," Schlegel said. After some hair-pulling, the problem turned out to be simple. "After we flipped the plus and minus signs in the program, everything worked perfectly."

The first public data release from SDSS-III is planned for December 2010 under the watchful eye of Mike Blanton at the New York University. "Making high-quality astronomical data available to all on the Web continues to revolutionize astronomical science and education, by taking advantage of the talents of not just our team, but of all astronomers and also the general public." Mike explains that the original SDSS data has already been used by others in thousands of research papers.

"This continues the legacy of the SDSS, one of the most productive astronomical surveys ever undertaken," said Jim Gunn of Princeton University, who will be awarded this month the National Medal for Science from President Obama for his pioneering work with the original SDSS.

"The leadership of this next generation of the SDSS has passed to the young scientists who did most of the hard work in SDSS I and II, and they have done a wonderful job, quickly and well. Bravo!"

About SDSS-III and BOSS

BOSS is the largest of four surveys in SDSS-III, which includes 350 scientists from 42 institutions. The BOSS design and implementation has been led from the U.S. Department of Energy's Lawrence Berkeley National Laboratory. The optical systems were designed and built at Johns Hopkins University, with new CCD cameras designed and built at Princeton University and the University of California at Santa Cruz/Lick Observatory. The University of Washington contributed new optical fiber systems, and Ohio State University designed and built an upgraded BOSS data-acquisition system. The "fully depleted" 16-megapixel CCDs for the red cameras evolved from Berkeley Lab research and were fabricated in Berkeley Lab's MicroSystems Laboratory (MSL).

Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy. The SDSS-III web site is http://www.sdss3.org/.

SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration, including the University of Arizona, the Brazilian Participation Group, University of Cambridge, University of Florida, the French Participation Group, the German Participation Group, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, the U.S. Department of Energy's Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, New Mexico State University, New York University, the Ohio State University, University of Portsmouth, Princeton University, University of Tokyo, the University of Utah, Vanderbilt University, University of Virginia, University of Washington and Yale University.

Contacts:

David Schlegel, BOSS Principal Investigator, Lawrence Berkeley National Laboratory, djschlegel@lbl.gov, 510-495-2595
Daniel Eisenstein, SDSS-III Director, University of Arizona, deisenstein@as.arizona.edu, 520-621-5904
Bob Nichol, SDSS-III Spokesperson, University of Portsmouth (UK), bob.nichol@port.ac.uk, +44 23 9284 3117
Paul Preuss, Communications Group, Lawrence Berkeley National Laboratory, paul_preuss@lbl.gov, 510-486-6249
Jordan Raddick, SDSS Public Information Officer, raddick@jhu.edu, 410-516-8889