The Dark Energy Survey Science Program

The Dark Energy Survey (DES) 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. This description of the Dark Energy Science Program, originally written as part of the DES proposal to NSF and DOE in December 2006, is organized as follows. We first present the forecast constraints on dark energy parameters; we then summarize each of the four proposed techniques for probing dark energy, describe how they will be implemented in DES, detail the primary systematic errors and how we plan to control them, list the assumptions underlying the parameter forecasts, and briefly mention ancillary science that can be done with each method. After describing other dark energy probes that DES will enable, we describe an extensive program of numerical simulations that will be used to nail down key theoretical undecertainties and that will serve as a testbed for developing DES analysis tools. We end by summarizing the photometric redshift (photo-z) estimates that are central to the entire DES science program. 1. Survey Parameters & Forecast Dark Energy Constraints 2 2. Galaxy Clusters 4 2.1 Galaxy Clusters in DES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2 Cluster Systematic Uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.3 Cluster Forecasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.4 Ancillary Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3. Weak Lensing 10 3.1 Weak Lensing in DES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.2 Weak Lensing Systematic Uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3.3 Weak Lensing Forecasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 4. Supernovae 16 4.1 Supernovae in DES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 4.1.1 Baseline SN Survey Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 4.1.2 Wide SN Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.2 Supernova Systematic Uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 4.3 Supernova Forecasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 4.4 Ancillary Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 5. Baryon Acoustic Oscillations 21 5.1 BAO in DES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 5.2 BAO Systematic uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 5.3 BAO Forecasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24