Unbiased Estimate of Dark Energy Density from Type Ia Supernova Data

December 2001 • 2001ApJ...562L.115W

Authors • Wang, Yun • Lovelace, Geoffrey

Abstract • Type Ia supernovae (SNe Ia) are currently the best probes of the dark energy in the universe. To constrain the nature of dark energy, we assume a flat universe and that the weak energy condition is satisfied, and we allow the density of dark energy, ρ_X(z), to be an arbitrary function of redshift. Using simulated data from a space-based SN pencil-beam survey, we find that by optimizing the number of parameters used to parameterize the dimensionless dark energy density, f(z)=ρ_X(z)/ρ_X(z=0), we can obtain an unbiased estimate of both f(z) and the fractional matter density of the universe, Ω_m. A plausible SN pencil-beam survey (with a square degree field of view and for an observational duration of 1 yr) can yield about 2000 SNe Ia with 0<=z<=2. Such a survey in space would yield SN peak luminosities with a combined intrinsic and observational dispersion of σ(m_int)=0.16 mag. We find that for such an idealized survey, Ω_m can be measured to 10% accuracy, and the dark energy density can be estimated to ~20% to z~1.5, and ~20%-40% to z~2, depending on the time dependence of the true dark energy density. Dark energy densities that vary more slowly can be more accurately measured. For the anticipated Supernova/Acceleration Probe (SNAP) mission, Ω_m can be measured to 14% accuracy, and the dark energy density can be estimated to ~20% to z~1.2. Our results suggest that SNAP may gain much sensitivity to the time dependence of the dark energy density and Ω_m by devoting more observational time to the central pencil-beam fields to obtain more SNe Ia at z>1.2. We use both a maximum likelihood analysis and a Monte Carlo analysis (when appropriate) to determine the errors of estimated parameters. We find that the Monte Carlo analysis gives a more accurate estimate of the dark energy density than the maximum likelihood analysis.

Links

• PDF https://iopscience.iop.org/article/10.1086/338142/pdf
• PREPRINT http://arxiv.org/abs/astro-ph/0109233
• SPIRES http://inspirehep.net/search?p=find+j+ASJOA,562,L115
• ELECTR https://doi.org/10.1086%2F338142
• SPIRES http://inspirehep.net/search?p=find+eprint+astro-ph/0109233