Dark energy properties from large future galaxy surveys

Abstract

We perform a detailed forecast on how well a {\sc Euclid}-like survey will be able to constrain dark energy and neutrino parameters from a combination of its cosmic shear power spectrum, galaxy power spectrum, and cluster mass function measurements. We find that the combination of these three probes vastly improves the survey's potential to measure the time evolution of dark energy. In terms of a dark energy figure-of-merit defined as $(σ(w_{\mathrm p}) σ(w_a))^{-1}$, we find a value of 690 for {\sc Euclid}-like data combined with {\sc Planck}-like measurements of the cosmic microwave background (CMB) anisotropies in a 10-dimensional cosmological parameter space, assuming a $Λ$CDM fiducial cosmology. For the more commonly used 7-parameter model, we find a figure-of-merit of 1900 for the same data combination. We consider also the survey's potential to measure dark energy perturbations in models wherein the dark energy is parameterised as a fluid with a nonstandard non-adiabatic sound speed, and find that in an \emph{optimistic} scenario in which $w_0$ deviates by as much as is currently observationally allowed from $-1$, models with $\hat{c}_\mathrm{s}^2 = 10^{-6}$ and $\hat{c}_\mathrm{s}^2 = 1$ can be distinguished at more than $2σ$ significance. We emphasise that constraints on the dark energy sound speed from cluster measurements are strongly dependent on the modelling of the cluster mass function; significantly weaker sensitivities ensue if we modify our model to include fewer features of nonlinear dark energy clustering. Finally, we find that the sum of neutrino masses can be measured with a $1 σ$ precision of 0.015~eV, (abridged)

Figures (5)

• Figure 1: The left panel shows the division into of the observed number of clusters into 7 redshift bins while keeping the cluster count common for all bins. The right panel shows the subsequent division of redshift bins $i=1,7$ into 7 mass bins, again with the stipulation that all mass bins contain the same number of clusters.
• Figure 2: Dependence of the posterior standard deviations, $\sigma$, for selected cosmological parameters for CMB+clusters on the number of redshift bins $N_z$ and mass bins $N_\mathrm{m}$. All numbers have been normalised to the corresponding $N_z=N_\mathrm{m} = 1$ result.
• Figure 3: Marginalised joint two-dimensional 68% and 95% credible contours from the CMB+clusters data set. The default redshift and mass binning configuration for the cluster data is $N_{\rm bin}=10$ (light red), but we also show the results for $N_{\rm bin}= 1$ bin (dark red) and 2 (red).
• Figure 4: Marginalised joint two-dimensional 68% and 95% credible contours from the CMB+clusters data set ("ccl", blue), CMB+shear+galaxies ("csgx", green), and all data sets ("csgxcl", black) for various parameters, using the default binning configuration of $N_{\rm bin}=10$ for the cluster data.
• Figure 5: Marginalised one-dimensional posterior probability density for $\log \hat{c}_\mathrm{s}^2$ for four different fiducial models (see labels in plots) from a "csgxcl" fit.