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Probing dark energy with the Large Synoptic Survey Telescope

Rendering of the LSST camera. SLAC National Accelerator Laboratory is leading the construction of the 3,200-megapixel camera, which will be the size of a small car and weigh more than three tons. Image courtesy SLAC National Accelerator Laboratory.

If you wear or have ever worn glasses, you know what it means to finally see with clarity. The Large Synoptic Survey Telescope (LSST) - currently under construction on Cerro Pachon near Vicuña,Chile - will give humanity a new set of 'glasses' to peer into the universe.

The construction of the LSST, led by the US Department of Energy's (DOE) SLAC National Accelerator Laboratory, may enable us to see billions of objects for the first time. Currently, most of the energy density of the universe is in unknown form. What's more, as a probe of dark energy and matter, the LSST is unique in its use of multiple cross-checking probes that reach unprecedented precision.

The LSST Dark Energy Science Collaboration (DESC) will produce about 30 Terabytes per night, which means the computing demands will be enormous. The total data volume expected will be on the order of several hundred Petabytes and require 100 TeraFlops of computing power. The DOE's Fermi National Accelerator Laboratory (Fermilab), in partnership with other institutions, is developing innovative software for scientists to explore the LSST's huge data sets.

Scott Dodelson, Fermilab astrophysicist, convened the DESC Software Working Group to design a software framework that will facilitate collaboration and use of LSST tools by all DESC scientists. The framework links software programs written specifically for the LSST with others written externally and runs them on Fermilab's FermiGrid, which in turn is connected to the US National Science Foundation's Open Science Grid (OSG).

Steve Kent, Jim Kowalkowski, Marc Paterno, and Saba Sehrish, all in Fermilab's Scientific Computing Division, developed the DESC framework and demonstrated it at the International Conference for High Performance Computing, Networking, Storage and Analysis (SC14). "The demo was an end-to-end simulation of LSST data and science analyses - that was the really important thing," says Kent. "It was a walk-through of all the steps with an eye on eventually expanding to the LSST scale."

Led by Sehrish, the group ran image simulations through the software framework and then through CosmoSIS, a cosmological parameter estimation program. "The scientists running the DESC workflows will not have to worry about details such as file transport or access to supercomputers to do their dark energy science," says Paterno. "We demonstrated how this could be done."

"LSST will truly be a next-generation survey. It will surpass preceding surveys in terms of data size in its first few months of operation," says University of Pennsylvania astrophysicist Bhuvnesh Jain, spokesperson for DESC. "The work of the Fermilab group is really going to pave the way for a new mode of doing software analyses and how people collaborate. I think it will have far-reaching implications for how we do cosmology."

- Greg Moore

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