Robust Dark Energy Constraints from Supernovae, Galaxy Clustering, and 3 yr<i>Wilkinson Microwave Anisotropy Probe</i>Observations

Abstract

Type Ia supernova (SN Ia), galaxy clustering, and cosmic microwave background\nanisotropy (CMB) data provide complementary constraints on the nature of the\ndark energy in the universe. We find that the three-year Wilkinson Microwave\nAnisotropy Probe (WMAP) observations give a CMB shift parameter of R =\n(\\Omega_m H_0^2)^{1/2} \\int_0^{z_{CMB}} dz'/H(z')= 1.70 \\pm 0.03. Using this\nnew measured value of the CMB shift parameter, together with the baryon\nacoustic oscillation (BAO) measurement from the Sloan Digital Sky Survey\n(SDSS), and SN Ia data from the HST/GOODS program and the first year Supernova\nLegacy Survey, we derive model-independent constraints on the dark energy\ndensity rho_X(z) and the cosmic expansion rate H(z). We also derive constraints\non the dark energy equation of state w_X(z)=w_0+w'z (with cutoff at z=2) and\nw_X(a)=w_0+(1-a)w_a.\n We find that current data provide slightly tighter constraints on rho_X(z)\nand H(z) as free functions in redshift, and roughly a factor of two improvement\nin constraining w_X(z). A cosmological constant remains consistent with data,\nhowever, uncertainties remain large for model-independent constraints of dark\nenergy. Significant increase in the number of observed SNe Ia between redshifts\nof 1 and 2, complemented by improved BAO and weak lensing cosmography\nmeasurements (as expected from the JEDI mission concept for the Joint Dark\nEnergy Mission), will be required to dramatically tighten model-independent\ndark energy constraints.\n