Projects: Dark Energy Survey (DES)
A critical research problem in cosmology is the need to understand the accelerating expansion of the Universe. This acceleration requires something new and strange---Dark Energy---which could arise from the energy of the vacuum (the cosmological constant) or a new ultra-light particle; alternatively it could indicate a flaw in Einstein's General Relativity, perhaps signaling that our three-dimensional world is embedded in a Universe of higher spatial dimensions. Any of these possibilities would represent a major shift in our current understanding of the nature of matter, energy, space, and time. In order to sort out the possibilities and pin down the nature of the dark energy, we need to make more precise measurements of its properties; the key property of dark energy that determines the expansion history of the Universe is its equation of state parameter, w, the ratio of its effective pressure to its energy density. In order to precisely measure w and its possible time evolution, we must build a powerful new instrument and a flexible and responsive data management system to accompany it, while continuing to develop improved methods of analysis.
We propose to address this problem with an astronomical survey, the Dark Energy Survey (DES), which will use a state of the art, wide-field, CCD imager and an existing telescope. We plan to carry out this survey using a new 3 deg2 CCD camera, DECam, mounted on the Blanco 4-m telescope at Cerro Tololo Inter-American Observatory (CTIO). We plan to build and deploy the new instrument, the Dark Energy Camera, and a powerful data management system with the support of Fermilab, NCSA, NOAO and the other partner institutions.
The Dark Energy Survey will enable measurements of the dark energy and dark matter densities and the dark energy equation of state through four independent methods: galaxy clusters, weak gravitational lensing, galaxy angular clustering (baryon acoustic oscillations), and supernovae. These methods, highlighted by the Dark Energy Task Force Report (DETF) as the most promising, are doubly complementary: they constrain different combinations of cosmological model parameters and are subject to different systematic errors. By exploiting this multiplicity, the DES will make a substantial and robust advance in the precision of dark energy measurements at the level envisioned for a DETF Stage III (i.e., near-term, intermediate-scale) experiment. It will also explore and develop methods to mitigate the systematic errors for the different dark energy methods.
The DES comprises two multi-band imaging surveys, a wide-field survey and a narrow time-domain survey. The wide-field survey covers 5000 sq. deg. in the south Galactic cap, completely encompassing the 4000 sq. deg. area of the South Pole Telescope (SPT) Sunyaev-Zel'dovich effect (SZE) survey, and reaches 24th magnitude in the griz filters. The depth and filter coverage of the wide-field survey are chosen primarily to achieve accurate galaxy and cluster photo-z measurements to redshifts z > 1. The wide-field survey will detect over 100,000 galaxy clusters and will measure shapes, photo-z's, and positions for 300 million galaxies.
The DES Supernova (SN) Survey involves frequent, repeat imaging of a much smaller area of sky to discover and measure large numbers of supernova light curves; the current SN survey strategy features deep imaging in the riz filters over 9 sq. deg. with a cadence of 5 visits per lunation, yielding good-quality light curves for over 1000 type Ia supernovae to redshift z~1.
