CU joins Sloan survey to map stars, galaxies etc. in 3D
By Jim Scott
The University of Colorado Boulder has become a full institutional member of the Sloan Digital Sky Survey-IV, an ambitious effort by some of the world’s top astronomers to map the celestial sky in three dimensions to learn more about the structure and evolution of the universe.
The survey, known as SDSS-IV, is the fourth stage of an effort that began with SDSS-I in 2000 to create the largest digital color image of the northern sky, said CU-Boulder Professor Michael Shull of the astrophysical and planetary sciences department, lead scientist in the effort by CU-Boulder to join the survey. Since 2000, astronomers have mapped about one-half of the visible northern sky in three dimensions as part of the three prior Sloan sky surveys, discovering nearly half a billion astronomical objects ranging from asteroids and stars to galaxies and distant quasars in the process.
“We got into this because we think it is going to be a great recruitment tool for new students, and we have one of the best undergraduate majors in the country,” Shull said. “We also want to recruit high-caliber graduate students and postdoctoral researchers.”
The SDSS 2.5-meter telescope is located at the Apache Point Observatory in Sunspot, N.M., and is owned by the Astrophysical Research Consortium, or ARC, an organization of eight research institutions including CU-Boulder. The Sloan telescope sky-mapping project is funded by the Alfred P. Sloan Foundation, the participating institutions, the National Science Foundation and the U.S. Department of Energy Office of Science. Apache Point also hosts several other telescopes, including a 3.5-meter optical telescope owned and operated by ARC and routinely used by CU-Boulder.
ARC was formed in 1984 to create a national observatory that could provide telescope time to each member university based on its investment. Current ARC members in addition to CU-Boulder are the University of Chicago, Johns Hopkins University, Princeton University, the Institute of Advanced Study in Princeton, N.J., the University of Washington, the University of Virginia and New Mexico State University. CU-Boulder owns a one-eighth share of each of the two telescopes.
The costs to build new instruments, make observations and analyze data from the SDSS-IV from 2014 to 2020 is estimated to be between $50 million and $60 million, said Shull. The Sloan Foundation is contributing roughly $10 million, while additional funds are coming from more than 10 full institutional members, including CU, and from scientists with individual and small group memberships from various institutions.
Full institutional partners like CU-Boulder are paying roughly $1 million to join part four of the Sloan sky survey effort. CU-Boulder’s member fee was supported by university grants, awards, donations, general funds and indirect cost recovery savings. As an early institutional partner joining the Sloan IV survey before the end of the current fiscal year, CU received a $350,000 discount from ARC, said Shull.
Light from the Sloan telescope is directed to two powerful new instruments — a dual-channel visible light, or optical spectrograph, and a near-infrared spectrograph. Astronomical spectrographs break light into telltale colors much like a prism, revealing information about the size, temperature, composition and motion of celestial objects, said Shull.
The Sloan spectrographs will carry out a massive survey of galaxies and quasars in the distant universe, as well as stars in the Milky Way and thousands of nearby galaxies, said Shull, who also is a member of CU-Boulder’s Center for Astrophysics and Space Astronomy.
The new optical spectrograph on the Sloan telescope can take data from up to 1,000 galaxies or quasars simultaneously, he said. The instrument includes a circular aluminum plate roughly the size of a large pizza pan with 1,000 small perforations precisely drilled to match up with known astronomical objects in the sky. Each hole is plugged with an optical fiber attached to the spectrograph.
“I think this is going to be a perfect way for undergraduates to get their hands dirty working with ‘big data,’ said Shull. “A lot of undergraduates are better at computers than we are, so hiring a freshman or a sophomore who really wants to get into computing and big data sets in the field of astronomy is one of our goals.”
One of the biggest discoveries by SDSS-III astronomers came in 2012 when they detected the predicted signature of the first sound waves from matter and radiation in the early universe, said Shull. Sloan researchers used a multi-fiber spectrograph as part of the Baryon Oscillation Sky Survey, or BOSS, to detect the large-scale structures of ancient galaxies — similar in some ways to ripples on a pond — that were preserved after the Big Bang.
Shull, who plans to use the multi-fiber spectrograph to hunt for distant quasars in the early universe going back 13 million years, said the BOSS effort also is expected to reveal new information about so-called “dark energy.” A hypothetical form of energy that makes up the majority of the universe and produces a force that opposes gravity, dark energy is thought to be the cause of the accelerating expansion of the universe.
Another SDSS-IV effort will be a sky survey in the infrared to probe the distribution, dynamics and chemistry of stars and to explore the formation of our Milky Way Galaxy and its two companion galaxies, the Large Magellanic Cloud and the Small Magellanic Cloud, said Shull. Since the two Magellanic Clouds are best viewed from the southern hemisphere, SDSS scientists plan to collaborate with astronomers who are using the 2.5 meter du Pont Telescope at Las Campanas, Chile, on the effort.
SDSS-IV astronomers also will be using the BOSS instrument to study the internal structure of 10,000 nearby galaxies. The data will include precise velocities of stellar motions and chemical abundances for a large range of galaxy masses, types and environments. The data will complement observations of two newly completed American telescopes: the ALMA millimeter and submillimeter array radio telescope in Chile and the Expanded-Very Large Array radio telescope in New Mexico.
SDSS-IV also has had a significant citizen science component since 2007, when a data set of a million galaxies was released to the public, who were asked to classify them in three categories: Elliptical galaxies, merging galaxies and spiral galaxies, including the direction of the spiral arms. An astounding 70,000 classifications were received by SDSS scientists from the public within an hour of the data release, and during the first year more than 150,000 people made more than 50 million galaxy classifications.
CU has a legacy in space dating back nearly 70 years, said CU-Boulder Vice Chancellor for Research Stein Sture. It is the top funded public university by NASA, has a $70 million instrument now flying on the Hubble Space Telescope, is leading a $485 million mission to Mars and controls four NASA satellites from campus.
A video news story on the project is available at http://youtu.be/1Rke59L5cAo.
Jim Scott is senior science editor for the CU Office of News Services.
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