February 12, 2015
Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)
In January 2015, the Sloan Digital Sky Survey III (SDSS-III), which several members of Kavli IPMU has been part of, released a latest public data “Data Release 12" (DR12) online. This data is the final release of the SDSS-III and available to the public. Weighing in at more than 100 Terabytes, DR12 contains measurements of the properties of nearly half a billion stars and galaxies, making it one of the largest and richest databases in the history of astronomy.
Fig.1: A still photo from an animated flythrough of the Universe using SDSS data. This image shows our Milky Way Galaxy. The galaxy shape is an artist's conception, and each of the small white dots is one of the hundreds of thousands of stars as seen by the SDSS.
Image credits: Dana Berry / SkyWorks Digital, Inc. and Jonathan Bird (Vanderbilt University)
http://www.sdss.org/wp-content/uploads/2015/01/milkyway.jpg
"The most astonishing feature of the SDSS is the breadth of ground-breaking research it enables," says Daniel Eisenstein of the Harvard-Smithsonian Center for Astrophysics, the Director of SDSS-III. "We've searched nearby stars for planets, probed the history of our Milky Way, and measured nine billion years of our Universe's accelerated expansion."
After a decade of design and construction, the SDSS began mapping the cosmos in 1998, using the dedicated 2.5-meter Sloan Foundation Telescope at Apache Point Observatory in New Mexico. SDSS-III started observations in July 2008 and completed its six-year, $45 million program in June 2014. The SDSS-III Collaboration includes 51 member institutions and a thousand scientists from around the world.
SDSS-III has devoted most of its 2000 nights of observing to measuring spectra: passing light from individual stars and galaxies through a fiber-optic spectrograph, which divides light into component wavelengths much like a prism separates light into the colors of the rainbow. "For each object that we observe, we're actually measuring several thousand light intensities at different wavelengths," says Jon Holtzman of New Mexico State University, which operates the Observatory on behalf of the consortium. "We can then pick out the light produced by particular kinds atoms and molecules, which lets us measure the motions and chemical compositions of stars and galaxies."
"Mapping out the elements in a star is like reading its DNA," says Steve Majewski of the University of Virginia. "We're using those DNA readings to decode the history of the Milky Way from the stars that we can observe today." Majewski is the Principal Investigator of APOGEE (the Apache Point Observatory Galactic Evolution Experiment), one of the four surveys that comprise SDSS-III. By looking in near-infrared wavelengths to see through obscuring dust clouds, APOGEE has mapped the distribution of 15 separate chemical elements in more than 100,000 stars, probing all regions of the Milky Way.
In addition to these elemental measurements from APOGEE, DR12 provides the first public release of data from MARVELS (the Multi-Object APO Radial Velocity Exoplanet Large-Area Survey). "MARVELS has made repeated measurements of 3000 stars to detect the back-and-forth motions that could reveal unseen orbiting planets," explains the project's Principal Investigator, Jian Ge of the University of Florida. "MARVELS is the first large-scale survey to measure these tiny motions for dozens of stars simultaneously," says Ge, "which means we can probe and characterize the full population of giant planets in ways that weren't possible before."
Fig.2：A still photo from an animated flythrough of the Universe using SDSS data. This image shows a small part of the large-scale structure of the Universe as seen by the SDSS - just a few of many millions of galaxies. The galaxies are shown in their proper positions from SDSS data.
Image credits: Dana Berry / SkyWorks Digital, Inc.
http://www.sdss.org/wp-content/uploads/2015/01/manygalaxies.jpg
DR12 also presents 3-dimensional maps of cosmic structure traced by galaxies and intergalactic hydrogen from the Baryon Oscillation Spectroscopic Survey (BOSS). "With these maps we've detected the fossil imprints of sound waves that filled the universe during the first half-million years after the Big Bang," explained BOSS Principal Investigator David Schlegel of Lawrence Berkeley National Laboratory.
The BOSS team is using those imprints to trace the expansion of the universe across nine billion years of cosmic history, with unprecedented precision. Their final analysis, expected later this year, "will provide the sharpest test yet for theories of dark energy and the accelerating universe," according to Schlegel.
On the other hand, the Sloan Extension for Galactic Understanding and Exploration (SEGUE), begun in SDSS-II and completed in SDSS-III, measured visible-light spectra of a quarter-million Milky Way stars. "With so many stars, SEGUE gives us a great map of structure in the outer Galaxy," says Constance Rockosi of the University of California at Santa Cruz, who led the SDSS-III component of SEGUE. "In combination with the much more detailed view of the inner Galaxy from APOGEE, we're getting a truly holistic picture of the Milky Way."
The DR12, which includes these observational data, is available to all the people as well as astronomers. This has been deeply related the history of the SDSS-III. "One of the most important decisions we made at the beginning of the SDSS was that we would release all of our data, so everyone could use it," says Alex Szalay of Johns Hopkins University, which developed the powerful online interfaces that most astronomers and many in the general public use to access SDSS data. "Nowadays we hear about Big Data left and right. The SDSS launched Big Data astronomy years before anyone was using that term."
"The DR12 is the richest dataset which we have ever had in astronomy," says Shun Saito, a project researcher of Kavli IPMU. "For instance BOSS, which I am involved in, has observed approximately a million of galaxies that shine much more brightly than our Milky Way. Such a gigantic 3-dimensional galaxy map allows us to analyze how strongly galaxies are clustering. This information can be used to test Einstein’s general relativity on cosmological scales like ~100 million light year, and even to weigh neutrinos which are thought be ones of the lightest elementary particles."
Alexie Leauthaud, a project assistant professor of Kavli IPMU, says, "DR12 marks the end of the BOSS survey and the tremendous achievement of the BOSS team which collected and analyzed more than 1.5 million spectra. Now we are looking ahead to plan the success of next generation Baryonic Acoustic Oscillation surveys such as PFS." The Subaru Prime Focus Spectrograph (PFS) is a ultra wide-field spectrograph which is scheduled to be installed at a prime focus of the Subaru Telescope in 2017. It is expected to reveal the history of an expanding universe through the precision survey of measuring distance to galaxies by the PFS. The Kavli IPMU is promoting the PFS project with international collaboration.
"Personally, data from BOSS has been a great boon for my research work which has focussed on combining this data with other deep imaging surveys to obtain astrophysical and cosmological constraints," says Surhud More, a project assistant professor of Kavli IPMU. "The ongoing Hyper Suprime-Cam Survey, which is a deep imaging survey with the Japanese Subaru Telescope, is designed to fully overlap with BOSS data. I expect the synergy between the two to improve our understanding of the Universe many-fold in the coming years."
While the SDSS-III completed in June 2014, SDSS-IV began in July 2014 on its six-year mission to study cosmology, galaxies, and the Milky Way. "Crossing the DR12 finish line is a huge accomplishment by hundreds of people," says Eisenstein. "But it's a big universe out there, so there is plenty more to observe."
Press Release of the SDSS-III
http://www.sdss.org/press/the-sloan-digital-sky-survey-opens-a-new-public-view-of-the-sky/
ABOUT THE SLOAN DIGITAL SKY SURVEY
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 Office of Science. The SDSS-III web site is 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, Brookhaven National Laboratory, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, The Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University.