Dark energy project moving forward

The Dark Energy Survey will study the nature of dark energy and cosmic acceleration.

The possibility that some cosmic dark energy exists that contributes to the expansion of the universe has been recognized for more than a decade. Although a dark force sounds like something from a science fiction movie, scientists now estimate that dark energy makes up 70 percent of our universe. The Dark Energy Survey (DES) will study the nature of dark energy and cosmic acceleration.

The project

The DES project will use four complementary techniques: a galaxy cluster survey in collaboration with the South Pole Telescope millimeter-wave cosmic microwave background mapping experiment; a cosmic shear measurement; a galaxy angular clustering measurement within redshift shells; and supernova distance measurements. These four complementary studies of the dark energy will move the field well beyond existing studies, delivering independent constraints on the nature of dark energy that are at least as precise as the best combined constraints available today. DES will use these techniques in two coupled surveys: a 5,000 square degree multiband, optical survey of the south galactic cap region, and a 40 square degree time domain search for supernovae.

DES is building an extremely red-sensitive 500-megapixel camera with a 1 meter diameter, a 2.2 degree field of view prime focus corrector, and a data acquisition system fast enough to take images in 17 seconds. The cage containing the system will be mounted at the prime focus of the Blanco 4-meter telescope at CTIO in Chile, and the instrument will become a general user instrument available to the astronomical community.

The DES data management system (DESDM) will be used to process and archive approximately 200 terabytes of raw imaging data into a few petabytes of science-ready data products. Under the leadership of NCSA research scientist Joe Mohr, who is also a University of Illinois astronomy and physics professor, and NCSA project manager Cristina Beldica, the DES collaboration will develop, deploy, and operate the DESDM system. This system consists of processing pipelines with built-in quality assurance testing, a distributed archive to support automated data processing and calibration within a high-performance computing environment, a catalog database to support calibration, provenance and science analyses, Web portals for control, monitoring, user data access and scientific analyses, and the hardware platforms required to operate the system. Full processing of a single season of data will require approximately 9.1 CPU-years and produce approximately 330 terabytes of data products, including catalogs of more than 5 billion objects.

Positive endorsements

NCSA and the Department of Astronomy at the University of Illinois at Urbana-Champaign received an initial grant of $650,000 from the National Science Foundation (NSF) for development of a data processing and archiving system. A continuation proposal to fully fund the DES data management development effort was submitted to NSF last December. In late January the DES project underwent a rigorous NSF-DOE joint review that evaluated all aspects of the project (technical, cost, schedule, management), progress to date, and proposed additional funding. The results of the review were very positive and the committee endorsed DES, recommending that it transition from the research and development phase into construction.

“This is exciting for us,” says Mohr, “because it means that after approximately three and a half years of R&D, DES is now—finally—on the construction path. That will lead us to a powerful new exploration of the cosmic acceleration.”

The timeline

The camera is being built by the Fermi National Accelerator Laboratory (Fermilab). The build phase for this project is 2004-2010, with the survey operations scheduled for 2011-2016. During the survey operations phase, NCSA will serve as the primary processing and archive center for the DES collaboration. NCSA’s high-capacity storage infrastructure will house both the raw and the processed data, and the center is also working on critical middleware and an accessible online archive for the DES data.

Data challenge

As part of the development of the data processing pipeline, NCSA and its collaborators recently concluded their third annual DES Data Challenge (DC3). The challenge tests the prototype processing system using simulated data provided by Fermilab. With each successive challenge, the simulated data become more sophisticated and more closely resemble the data that will be gathered starting in 2011.

During DC3, the DESDM team successfully processed, calibrated, and archived 10 nights of simulated DECam images, equivalent to 20 percent of the full Sloan Digital Sky Survey imaging dataset. Images and catalog files were ingested to the database files table, such that in the end about 400 million objects were cataloged and ingested. Total data volume after processing is about 33 terabytes. The processing was carried out on the TeraGrid high-performance computing platforms, primarily the Mercury cluster at NCSA and the IA64 cluster at the San Diego Supercomputing Center (SDSC), and the image and catalog data products were transferred to a dedicated repository on gpfs-wan at SDSC.

“Solutions were developed to overcome bottlenecks in the ingestion, and the overall the data quality from the current version of the system was quite good,” says Mohr.

DES collaborators

• Argonne National Laboratory
• Cerro Tololo Interamerican Observatory (Chile)
• Fermi National Accelerator Laboratory (Fermilab)
• Institut d’Estudie Espacials de Catalunya and Institut de Fisica d’Altes Energies (Spain)
• Lawrence Berkeley National Laboratory
• Observatorio Nacional de Brazil
• University College London, Cambridge, Edinburgh, and Portsmouth, UK
• University of Chicago
• University of Illinois at Urbana-Champaign
• University of Michigan

DES data management team
NCSA/University of Illinois at Urbana-Champaign
Joe Mohr
Cristina Beldica
Darren Adams
Dora Cai
Anthony Darnell
Greg Daues
Michelle Gower
Choong Ngeow
Alex Parga

Fermilab
Douglas Tucker
Nikolay Kiropatkin
Huan Lin
Eric Nielsen
Chris Stoughton

Observatorio Nacional de Brazil
Luiz da Costa
Leandro Martelli
Ricardo Ogando
Bruno Rossetto

Institut d’Astrophysique, Paris
Emmanuel Bertin

New York University
Erin Sheldon

University of Pennsylvania
Mike Jarvis

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