The Dark Energy Survey (DES) is an intermediate term survey, in the years 2011-2016, that will address the nature of dark energy using four independent and complementary techniques: (1) a galaxy cluster survey in collaboration with NSF's South Pole Telescope Sunyaev-Zel'dovich Effect mapping experiment, (2) a cosmic shear measurement, (3) a galaxy angular clustering measurement within redshift shells to z=1.35, and (4) distance measurements to approximately 2000 type 1a supernovae (SNe Ia). The DES will produce about 170Tb of raw data, processed into science-ready images and catalogs and co-added into deeper, higher quality images and catalogs. In total, the DES dataset will approach 2Pb. This data volume and the survey duration require a new type of data management system with a high degree of automation and robustness, including integrated quality assurance testing. The present collaborative project will build the DES Data Management (DESDM) system. DESDM has been designed and tested, using both simulated data and real data from the Mosaic2 camera. The project team has created working prototypes of many elements of DESDM and will now transform those prototypes into the production version of the DESDM system.
DES is a complex international, multi-agency project, with far-reaching foreign and domestic impacts. It is organized into DESDM and two other themes. These are the Dark Energy Camera (DECam), to be installed at the 4-meter Blanco telescope of the Cerro Tololo Interamerican Observatory (CTIO), and the facilities improvement and integration project at the CTIO (CTIOFP). The CTIOFP is supported by CTIO, a component of NSF's National Optical Astronomy Observatory, and DECam is supported by the Department of Energy (DoE) and by international and institutional partners. DESDM is supported by NSF and also by the project partners.
The DESDM project is working collaboratively with other large scale imaging projects to develop common solutions, and will be making all produced software available to the community. Students will play important role, developing expertise in aspects of scientific data management, high performance computing, and the development of science analysis tools. The DESDM system will archive the DES data, enabling public access and science analyses (after a one year proprietary period) through a provided scientific analysis interface that will use high performance computing resources at the NSF's National Center for Supercomputing Applications (NCSA), operated by the University of Illinois. A separate part of the project not covered by this award is a DECam Reduction Portal, supporting non-DES users of the DECam to reduce their own data.
The Dark Energy Survey (DES) is an upcoming optical survey at Cerro Tololo, Chile, that will commence operation in September, 2013. One of the primary goals of the survey will be to constrain the properties and history of the strange accelleration of the universe, the cause of which has been dubbed "dark energy" (mostly a description of our ignorance, rather than a truly informative name). One of the key methods we plan to emply for studying dark energy is a technique called weak gravitational lensing. This is where the light from distant galaxies get bent slightly by the gravitational force from other mass concentrations in the universe that the photons pass on their way to earth. By studying the shapes of these distant galaxies, we can learn about statistical properties of how masses are distributed in the universe. More importantly, we can study this effect as a function of distance to the masses, which give us a historical view of how the mass distributions have changed over time. It is one of the few direct ways to study dark matter, since the effect does not rely on the masses glowing on their own, so it is a very powerful technique. Unfortunately, the effect is also very weak. The shapes of distant galaxies typically only change by a few percent, so we need to look at lots of galaxies to be able to tease out the effects we are looking for. Additionally, there are many other ways for the galaxy to be stretched slightly: the atmospheric "twinkling", distortion in the telescope, tracking errors, various electronic effects in the camera, etc. This project has been to write software that can accurately correct for all of these different spurious shape effects for the Dark Energy Survey telescope and camera, so that we can produce catalogs of galaxy shapes that are usable for weak gravitational lensing analyses. The code has been completed, including both a measurement on a single image that can be run as soon as each image from the telescope has been processed, and also a measurement for each galaxy that uses all of the images taken for that galaxy in an optimal way. Another innovative algorithm was our technique for using all the images taken during the survey to more accurately estimate the effect of the optics. Some of the effort has been merely to make sure the software handles the kind of data being generated by the Dark Energy Camera (a new camera built for DES). However, much of the research effort has been to get the shear accuracy down to the limits required for DES, since it will achieve much greater statistical power than any other weak lensing survey to date, and we don't want inaccuracies in the shear measurements to dominate the final error budget. Hence the need for the innovative algorithms described above. We have been testing the code primarily on simulated data, trying to find all the ways that the code might not completely correct for all the different important effects. While we still have some concerns about the accuracy in a couple respects, we are very close to achieving the required accuracy for the first year data (where the requirements will not be as stringent). Making the code accurate enough for the full 5 years worth of data will require more work, and is the subject of a subsequent NSF grant for "DES Operations".
