LSST precision on Dark Enery Parameters based on recent results with WMAP3 normalization:
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σ(wa) X σ(wp) as a function of the time-throughput product A Ω t. The assumptions are given as follows.
We show the constraints of three different probes: supernovae, baryon acoustic oscillations, and weak lensing. These probes can measure the distance-redshift relationship and thus the expansion of the universe, which is sensitive to cosmological parameters. In addition, weak lensing can also measure the growth of the large-scale structure.
For SNe, we assume a "drilled" survey of three fields (10 sq. deg each). LSST will repeatedly observe these three fields with sufficiently short cadence to obtain 2000 z < 0.8 SNe every year with well-followed multicolor light curves. Photo-zs of these SNe are expected to be much better than those of galaxies. To forecast SN constraints on dark energy, we have included 1% (3%) uncertainties due to SN evolution in the optimistic (pessimistic) case. The evolution uncertainties can severely impact dark energy constraints from SNe. We have also included photometry errors and k-correction errors at 0.01~0.02 mag level, which are sub-dominant to evolution and photo-z uncertainties.
Photo-z for SNe:
- In the optimistic case, the uncertainty in the photo-z bias reduces from 0.0025(1+z) to 0.0005(1+z) by a constant factor each year.
- In the pessimistic case, the uncertainty in the photo-z bias reduces from 0.005(1+z) to 0.001(1+z) by a constant factor each year.
Photo-z for Galaxies:
- In the optimistic case, the uncertainty in the photo-z bias reduces from 0.01(1+z) to 0.0025(1+z) by a constant factor each year. The uncertainty in the rms: σz = 0.04 (1+z), σ(σz) = sqrt(2)*σ(zbias).
- In the pessimistic case, the uncertainty in the photo-z bias reduces from 0.02(1+z) to 0.005(1+z) by a constant factor each year and rms: σz = 0.06 (1+z), σ(σz) = sqrt(2)*σ(zbias).
Galaxy number density:
- The galaxy number density follows n(z) = n0 z2 Exp(-z/z0) with z0 from 0.35 to 0.5 linearly in 10 years.
- We adjust n0 so that the projected number density (z = 0--3.5) increases linearly from 11 to 50 per sq. arcmin in 10 years.
Galaxy biases: σ(gal bias) stays at 15% error. This is the error level from current low-z observations (galaxy bispectrum, Verde et al. 2002).
Weak Lensing:
- 10 tomographic bins + 80 photo-z parameters (40 rms + 40 bias)
- (galaxy rms shear)2 = (0.18 + .042*z)2
- shear systematics:
- optimistic case: σ(γ) = 0.0005 / # years
- Pessimistic case: σ(γ) = 0.005 / # years
BAO:
- 40 bins + 80 photo-z parameters (40 rms + 40 bias)
- 40 galaxy clustering bias parameters
Parameters: w0, wa, ωm, ωb, angular size of the sound horizon at the last scattering surface, Ωk, primordial helium fraction, initial matter power spectrum tilt, normalization of the power spectrum, photo-z parameters, and galaxy clustering bias (BAO only).
Planck priors are included and the result for w0 & wa is marginalized over all other parameters.