Robust Dark Energy Constraints from Supernovae, Galaxy Clustering, and 3 yrWilkinson Microwave Anisotropy ProbeObservations

Type Ia supernova (SN Ia), galaxy clustering, and cosmic microwave background anisotropy (CMB) data provide complementary constraints on the nature of the dark energy in the universe. We find that the three-year Wilkinson Microwave Anisotropy Probe (WMAP) observations give a CMB shift parameter of R = (ₘ H₀²) ^1/2 ₀^z₂₌₁ dz'/H (z') = 1. 70 0. 03. Using this new measured value of the CMB shift parameter, together with the baryon acoustic oscillation (BAO) measurement from the Sloan Digital Sky Survey (SDSS), and SN Ia data from the HST/GOODS program and the first year Supernova Legacy Survey, we derive model-independent constraints on the dark energy density rhoX (z) and the cosmic expansion rate H (z). We also derive constraints on the dark energy equation of state wX (z) =w₀+w'z (with cutoff at z=2) and wX (a) =w₀+ (1-a) wₐ. We find that current data provide slightly tighter constraints on rhoX (z) and H (z) as free functions in redshift, and roughly a factor of two improvement in constraining wX (z). A cosmological constant remains consistent with data, however, uncertainties remain large for model-independent constraints of dark energy. Significant increase in the number of observed SNe Ia between redshifts of 1 and 2, complemented by improved BAO and weak lensing cosmography measurements (as expected from the JEDI mission concept for the Joint Dark Energy Mission), will be required to dramatically tighten model-independent dark energy constraints.