0 Assigned ID: 1734 ----- Attempting Submission 1 (Fri Mar 01 20:25:37 GMT 2013) ----- HST Phase I Proposal 1734 (GrismDEProp.apt) successfully submitted. ----- Attempting Submission 2 (Fri Mar 01 21:06:46 GMT 2013) ----- Understanding the accelerating expansion of the universe is widely regarded as one of the most important problems in physics. As a result there are several very large future surveys planned that aim make precise measurements of the properties of this "dark energy". Two of the most ambitious are the satellite missions WFIRST and Euclid, both of which intend to undertake enormous galaxy redshift surveys of emission line galaxies at z > 0.7 using near-IR low resolution slitless spectroscopy. In order to properly plan and optimize these ambitious projects one needs to know the number and clustering amplitude of these emission line galaxies, how these depends on redshift and line flux, and how well low resolution slitless spectroscopy performs at acquiring reliable redshifts. Currently all of these are poorly known. Fortunately the WFC3 G141 grism is closely matched to the current instrumental designs of WFIRST and Euclid providing a unique resource with which to answer these questions. The data already taken for the 3D-HST Treasury survey provide more than enough depth and sufficient area to make the required space density and clustering measurements to effectively answer these questions. Further, the multi-band photometry available in these fields greatly helps with redshift measurements, allowing a precise analysis of the likely redshift completeness that can be obtained from just the G141 grism and which additional photometric bands are optimal for redshift success. We propose to use this archival grism data to make these measurements using the findings to investigate the survey design trade offs and find optimal survey designs for a future space based dark energy survey. COSMOLOGY 12 Medium false false 0.0 0.0 false false false SUPPORTED