Dark Energy Survey Publicly Releases Data Trove

Scientists on the Dark Energy Survey (DES) publicly released data from the project’s first three years during a special session held at the American Astronomical Society meeting in Washington DC. The release includes information on about 400 million astronomical objects, from distant galaxies billions of light-years away to stars in our own galaxy.

The public release fulfills a commitment scientists on the survey made to share 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 roughly 40,000 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.

DES scientists are using this data to learn more about dark energy, the mysterious force believed to be accelerating the expansion of the universe, but wanted astronomers and the public to have access for other pursuits. “There are all kinds of discoveries waiting to be found in the data,” says Brian Yanny, a scientist at Fermi National Accelerator Laboratory (CSA CSM) and member of the DES data management project. “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 Dark Energy Camera is mounted on the Blanco telescope in Chile. Photo: Fermilab

The Dark Energy Camera is mounted on the Blanco telescope in Chile. Photo: Fermilab

The Dark Energy Camera, the primary observation tool of the Dark Energy Survey, is one of the most powerful digital imaging devices in existence. It was built and tested at Fermilab, the lead laboratory on the Dark Energy Survey, and is mounted on the National Science Foundation’s Blanco telescope, part of the Cerro Tololo Inter-American Observatory in Chile, a division of NOAO. The DES images are processed by a team at the National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign. The DES data can be accessed online, together with papers drawn from the first years of DES data.

“We’re excited that this release of high-quality imaging data is now accessible to researchers around the world,” says Matias Carrasco Kind, a DES release scientist at NCSA. “While DES was designed with the goal of understanding dark energy and dark matter, the huge amount of data in these images and catalogs will bring new scientific applications, challenges and opportunities for discovery to astronomers and data scientists. In collaboration, NCSA, NOAO and the LIneA group in Brazil are providing the tools and resources to access and analyze this rich and robust data set.”

One new discovery enabled by the data set is the detection of 11 new streams of stars around our Milky Way. A massive halo of dark matter surrounds the Milky Way, exerting 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,” says Alex Drlica-Wagner, an astrophysicist at 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 DES findings, researchers had discovered about two dozen stellar streams, many of them using the Sloan Digital Sky Survey, a precursor to the Dark Energy Survey. “We’re interested in these streams because they teach us about the formation and structure of the Milky Way and its dark matter halo,” says Nora Shipp, a graduate student from the University of Chicago who led the effort to detect new stellar streams. “Stellar streams give us a snapshot of a larger galaxy being built out of smaller ones. These discoveries are possible because DES is the widest, deepest and best-calibrated survey out there.”

Since there is no universally accepted naming convention for stellar streams, the Dark Energy Survey has reached out to schools in Chile and Australia, asking young students to select names. Students and teachers there have worked together to name the streams after aquatic words in native languages from northern Chile and aboriginal Australia.

DES plans one more major public data release, after the survey is completed, which will include nearly twice as many exposures as in this release. “This result is an excellent example of how data mining—the exploration of large data sets—leads to new discoveries,” says Richard Green, director of the National Science Foundation’s (NSF) Division of Astronomical Sciences. “NSF is investing in this approach through our foundation-wide ‘Harnessing the Data Revolution’ initiative, which is encouraging fundamental research in data science. We’re expecting a drumbeat of exciting discoveries, particularly when the Large Synoptic Survey Telescope data floodgates are opened!”