A New Search for Dark Energy Begins
Photograph of Senior Operations Engineer Dan Long loading the first Baryon Oscillation Spectroscopic Survey instrument cartridge of the night into the Sloan Digital Sky Survey telescope. The cartridge holds a "plug-plate" at the top, which positions a thousand optical fibers (red and blue). These cartridges are locked into the base of the telescope and are changed many times during a night. Credit: Dan Long, Apache Point Observatory
The most ambitious attempt yet to trace the history of the universe has seen "first light." Two Penn State scientists, Professors of Astronomy Niel Brandt and Donald Schneider, are members of the Baryon Oscillation Spectroscopic Survey (BOSS), a part of the Sloan Digital Sky Survey III (SDSS-III), which has begun a quest to collect electro-magnetic spectra for 1.4 million galaxies and 160,000 quasars by 2014. "These observations should provide quite accurate measurements of the expansion history of the universe, and thus should reveal the relative importance of ordinary matter, dark matter, and dark energy over a wide range of cosmic time," said Brandt.
To achieve the survey's first-light milestone after years of preparations, the SDSS-III team used new, specially-built spectrograph instruments installed on the Sloan Foundation 2.5-meter telescope at Apache Point Observatory in New Mexico. On the night of September 14-15, the team used the new instruments to measure the spectra of a thousand galaxies and quasars. The first data from the new spectrographs 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." Ross, who for the past year has been leading the BOSS quasar-target-selection effort as a postdoctoral scholar at Penn State, moved to the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) in early September.
Schneider, who is the SDSS-III Survey Coordinator, and Brandt plan to involve Penn State undergraduate students, graduate students, and postdoctoral research associates in the analysis of BOSS data. "In addition to the primary goal of measuring the properties of dark energy, the BOSS data will provide a wealth of data on a wide range of other scientific questions," said Brandt. Brandt is leading the BOSS effort in two areas: the identification of sources of X-ray emission, and a study of the variability of winds from quasars.
"The data from BOSS will be the best data ever obtained on the large-scale structure of the universe," said David Schlegel of Berkeley Lab, the Principal Investigator of BOSS. BOSS uses the same telescope as the original Sloan Digital Sky Survey, but it uses 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."
One of the Baryon Oscillation Spectroscopic Survey cartridges containing 1,000 optical fibers, which guide light from a "plug plate" targeting specific galaxies and quasars to the spectrograph. The Sloan Foundation telescope is in background. Credit: Dan Long, Apache Point Observatory
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 earthquake waves passing through rock, these pressure waves pushed some of the matter in the universe closer together as they traveled, and left some of the matter farther apart" explains Nikhil Padmanabhan, a BOSS researcher who recently moved from Berkeley Lab to Yale University. "When the universe was only a few hundred thousand years old, the universe cooled enough to halt the waves, leaving imprints 500 million light years long that has lasted until the present day."
"We can see this frozen wave 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."
"Studying baryon oscillations is an exciting method for measuring dark energy in a way that's complementary to techniques in supernova cosmology," said Schlegel. "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 spectrographs work with more than two thousand metal plates that fit over the telescope; all these plates will mark 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.
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. The light energy from quasars is thought to result from matter falling into supermassive black holes in distant galaxies. This quasar was one of approximately 200 among the thousand quasars and galaxies whose spectra were obtained in the first-light exposure. At bottom is the BOSS spectrum of the object, which allows astronomers to measure its redshift. BOSS plans to collect millions of such spectra and use the distances derived from them to map the geometry of the universe. Credit: David Hogg, Vaishali Bhardwaj, and Nic Ross
Using these plug plates for the first light image was fast and 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. Making high-quality astronomical data available to all on the Web, with no need to spend nights awake at a mountaintop telescope, promises a revolution in astronomical science and education. "This continues the legacy of the SDSS, one of the most productive astronomical surveys ever undertaken," said Jim Gunn of Princeton University, who recently was awarded the Presidential Medal for Science 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!"
CONTACTS AT PENN STATE:
Barbara Kennedy, Eberly College of Science Public Information Officer, science@psu.edu, 814-863-4682
Niel Brandt, BOSS Participant, nbrandt@astro.psu.edu, 814-865-3509
Donald Schneider, SDSS-III Survey Coordinator, dps@astro.psu.edu, 814-863-9554
CONTACTS AT THE SDSS PROJECT:
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
ABOUT SDSS-III AND BOSS:
BOSS is the largest of four surveys in SDSS-III, which includes 350 scientists from 42 institutions. BOSS's principal investigator is David Schlegel, its survey scientist is Martin White, and its instrument scientist is Natalie Roe; all three are with the Physics Division of the U.S. Department of Energy's Lawrence Berkeley National Laboratory. Daniel Eisenstein of the University of Arizona is the director of SDSS-III.
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: 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, and the University of Washington.
The extensive upgrade to the SDSS spectrographs and fiber cartridges was supported in large part by competitive grants to the SDSS-III collaboration from the Office of High-Energy Physics in DOE =EDs Office of Science, which will also be helping to support the ongoing operations of BOSS in SDSS-III. 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 unique "fully depleted" 16-megapixel CCDs for the red cameras evolved from Berkeley Lab research and development on radiation-hard particle detectors for high-energy physics experiments and were fabricated in Berkeley Lab=EDs MicroSystems Laboratory (MSL). Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research for DOE=EDs Office of Science and is managed by the University of California. Visit our website at http://www.lbl.gov