Jan. 11, 2018 — Researchers around the world can now explore the first three years of data from the Dark Energy Survey (DES) processed at the National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign. At a special session held during the American Astronomical Society meeting in Washington, D.C., scientists on the Dark Energy Survey announced the first major release of data from the survey including information on more than 400 million astronomical objects, including distant galaxies billions of light years away as well as stars in our own galaxy.
DES scientists are using this data, collected as part of the largest and deepest cosmological survey to date, to learn more about dark energy, the mysterious force believed to be accelerating the expansion of the universe. The survey enables astronomers to map out the galaxy distribution half-way back in cosmic time, which represents a major breakthrough in survey science and will enable many scholarly achievements in the future.
The Dark Energy Camera, the primary observation tool of DES, is one of the most powerful digital imaging devices in existence. It was built and tested at Fermilab, the lead laboratory on DES, and is mounted on the National Science Foundation’s (NSF) 4-meter Blanco telescope, part of the Cerro Tololo Inter-American Observatory in Chile, a division of the National Optical Astronomy Observatory (NOAO).
The images captured by the DECam are then sent to NCSA’s Dark Energy Survey Data Management (DESDM) Project, which has been fully developed and operated by NCSA with support from NSF. The DESDM system processes and calibrates the DES data and the DECam Community Pipeline, used by NOAO to process DECam data obtained by non-DES observers.
The DES images captured each night are received in large volumes of observations over high-speed networks from the telescope in Chile. Using the Blue Waters supercomputer, Illinois Campus Cluster Program, and Open Science Grid at Fermilab, the DESDM team first processes all of the images. After each individual exposure has been processed, the DESDM team combines all of the images with the help of Blue Waters in order to create a full and deep map of the southern sky, allowing the DES project to achieve depth. Through the efforts of NCSA’s DESDM team, the raw data generated by the DECAM instrument at the CTIO observatory is turned into science-ready data products.
“We’re excited that this anticipated release of high-quality imaging and catalog data is now accessible to researchers around the world. While this project was designed with the goal of understanding dark energy and dark matter, the huge amount of data in images and catalogs, processed at the National Center for Supercomputing Applications (NCSA) at Illinois, will bring new scientific applications, challenges and opportunities for discovery not only to astronomers but also data scientists,” said Matias Carrasco Kind, Release Scientist for the Dark Energy Survey and member of the DESDM team at NCSA, who coordinated this release. “This was truly a collaborative effort from many DES members and institutions around the world,” he added.
“This is an outstanding collective achievement and with the help of NOAO and LIneA we are providing the tools and resources to access and analyze this rich and robust data in an unprecedented partnership,” added Don Petravick, Principal Investigator for the DESDM team at NCSA.
“NCSA recognized many years ago the key role that advanced computing and data management would have in astronomy and is thrilled with the results of this collaboration with campus and our partners at Fermilab and the National Optical Astronomy Observatory,” said NCSA Director Bill Gropp. NCSA’s commitment to astronomy reaches beyond DES, however, as they will also serve as the global central hub and data center for the Large Synoptic Survey Telescope (LSST) project, the next generation survey which is set to be fully operational in 2023.
In addition to announcing the public release of their data, DES scientists shared some of their preliminary cosmological findings in the special session at the American Astronomical Society meeting today, such as the discovery of a dozen new stellar streams, remnants of smaller galaxies torn apart and devoured by our Milky Way.
The public release of the first three years of DES data fulfills the project’s commitment to sharing their findings with the astronomy community and the public. The data cover the full DES footprint—about 5,000 square degrees, or one eighth of the entire sky—and include more than 38,000 exposures taken with the Dark Energy Camera. The images correspond to hundreds of terabytes of data and are being released along with catalogs of hundreds of millions of galaxies and stars.
“There are all kinds of discoveries waiting to be found in the data,” said Dark Energy Survey Director Josh Frieman of the U.S. Department of Energy’s Fermi National Accelerator Laboratory. “While DES scientists are focused on using it to learn about dark energy, we wanted to enable astronomers to explore these images in new ways, to improve our understanding of the universe.”
“The great thing about a big astronomical survey like this is that it also opens a door to many other studies, like the new stellar streams,” added Adam Bolton, Associate Director for the Community Science and Data Center at NOAO. “With the DES data now available as a ‘digital sky,’ accessible to all, my hope is that these data will lead to the crowdsourcing of new and unexpected discoveries.”
The DES data can be accessed online from the NCSA site.
One new discovery enabled by the data set is the detection of roughly a dozen new streams of stars around our Milky Way. Our home galaxy is surrounded by a massive halo of dark matter, which exerts a powerful gravitational pull on smaller, nearby galaxies. The Milky Way grows by pulling in, ripping apart and absorbing these smaller systems. As stars are torn away, they form streams across the sky that can be detected using the Dark Energy Camera. Even so, stellar streams are extremely difficult to find since they are composed of relatively few stars spread out over a large area of sky.
“It’s exciting that we found so many stellar streams,” said astrophysicist Alex Drlica-Wagner of Fermilab. “We can use these streams to measure the amount, distribution, and clumpiness of dark matter in the Milky Way. Studies of stellar streams will help constrain the fundamental properties of dark matter.”
Prior to the new discoveries by DES, only about two dozen stellar streams had been discovered. Many of them were found by the Sloan Digital Sky Survey, a precursor to the Dark Energy Survey. The effort to detect new stellar streams in the Dark Energy Survey was led by University of Chicago graduate student Nora Shipp.
“We’re interested in these streams because they teach us about the formation and structure of the Milky Way and its dark matter halo. Stellar streams give us a snapshot of a larger galaxy being built out of smaller ones,” said Shipp. “These discoveries are possible because DES is the widest, deepest and best-calibrated survey out there.”
Other DES work concerns quasars, the supermassive black holes in the the middle of many galaxies. While the black holes themselves give off almost no light, a huge surrounding disk of inspiraling material can make quasars some of the brightest objects in the universe. It was long thought that these massive disks could only change slowly and would be stable for thousands or even millions of years. But recently, astronomers began noticing that some rare quasars became brighter or dimmer by factors of 2 or even 10 in only a few years.
Dr. Nick Rumbaugh and Prof. Yue Shen at the University of Illinois at Urbana-Champaign used DES data to study for these Extremely Variable Quasars. They identified 977 quasars with massive luminosity changes that occurred in only fifteen years or less. Their work suggests than many if not most quasars routinely undergo such wild changes. What’s more, it suggests that this variability is a normal part of a quasar’s life cycle and not due to a passing galactic cloud obscuring the quasar or a star suddenly slamming into the black hole.
Currently in its fifth year of observation, DES plans one more major public data release after the survey is completed. The second release will be the same one eighth of the sky but much deeper and more detailed.
This work is supported in part by the U.S. Department of Energy Office of Science.
The Dark Energy Survey (DES) is a collaboration of more than 400 scientists from 26 institutions in seven countries. Funding for the DES Projects has been provided by the U.S. Department of Energy Office of Science, U.S. National Science Foundation, Ministry of Science and Education of Spain, Science and Technology Facilities Council of the United Kingdom, Higher Education Funding Council for England, ETH Zurich for Switzerland, National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, Kavli Institute of Cosmological Physics at the University of Chicago, Center for Cosmology and AstroParticle Physics at Ohio State University, Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and Ministério da Ciência e Tecnologia, Deutsche Forschungsgemeinschaft, and the collaborating institutions in the Dark Energy Survey, the list of which can be found at www.darkenergysurvey.org/collaboration.