Dark Energy Survey Year 1 Results: Constraints on Extended Cosmological Models from Galaxy Clustering and Weak Lensing

TL;DR

This work extends DES Y1 analyses to four beyond-ΛCDM scenarios by jointly analyzing galaxy clustering, weak lensing, and galaxy–galaxy lensing with external data from Planck, BAO/RSD, and Pantheon SNe. The authors show that DES Y1 alone is largely consistent with ΛCDM and GR, while DES data notably strengthen constraints on modified gravity (Σ0, μ0) when combined with external probes, and tighten the upper limit on N_eff and the curvature parameter. Across the extensions, no statistically significant evidence for time variation in the dark energy equation of state or deviations from GR is found; the combined DES+external constraints favor GR and a standard N_eff ≈ 3.046. The analysis emphasizes rigorous validation and blinding and sets the stage for substantially improved constraints with DES Year 3 data.

Abstract

We present constraints on extensions of the minimal cosmological models dominated by dark matter and dark energy, $Λ$CDM and $w$CDM, by using a combined analysis of galaxy clustering and weak gravitational lensing from the first-year data of the Dark Energy Survey (DES Y1) in combination with external data. We consider four extensions of the minimal dark energy-dominated scenarios: 1) nonzero curvature $Ω_k$, 2) number of relativistic species $N_{\rm eff}$ different from the standard value of 3.046, 3) time-varying equation-of-state of dark energy described by the parameters $w_0$ and $w_a$ (alternatively quoted by the values at the pivot redshift, $w_p$, and $w_a$), and 4) modified gravity described by the parameters $μ_0$ and $Σ_0$ that modify the metric potentials. We also consider external information from Planck CMB measurements; BAO measurements from SDSS, 6dF, and BOSS; RSD measurements from BOSS; and SNIa information from the Pantheon compilation. Constraints on curvature and the number of relativistic species are dominated by the external data; when these are combined with DES Y1, we find $Ω_k=0.0020^{+0.0037}_{-0.0032}$ at the 68% confidence level, and $N_{\rm eff}<3.28\, (3.55)$ at 68% (95%) confidence. For the time-varying equation-of-state, we find the pivot value $(w_p, w_a)=(-0.91^{+0.19}_{-0.23}, -0.57^{+0.93}_{-1.11})$ at pivot redshift $z_p=0.27$ from DES alone, and $(w_p, w_a)=(-1.01^{+0.04}_{-0.04}, -0.28^{+0.37}_{-0.48})$ at $z_p=0.20$ from DES Y1 combined with external data; in either case we find no evidence for the temporal variation of the equation of state. For modified gravity, we find the present-day value of the relevant parameters to be $Σ_0= 0.43^{+0.28}_{-0.29}$ from DES Y1 alone, and $(Σ_0, μ_0)=(0.06^{+0.08}_{-0.07}, -0.11^{+0.42}_{-0.46})$ from DES Y1 combined with external data, consistent with predictions from GR.

Figures (8)

• Figure 1: Estimated redshift distributions of the lens and source galaxies used in the analysis. The shaded vertical regions define the bins: galaxies are placed in the bin spanning their mean photo-$z$ estimate. We show both the redshift distributions of galaxies in each bin (colored lines) and their overall redshift distributions (black lines).
• Figure 2: Impact of assumptions and approximations adopted in our analysis, demonstrated on synthetic data (that is, noiseless DES data centered on the theoretical expectation, along with actual external data). Each column shows one of the cosmological parameters describing $\Lambda$CDM extensions; the dotted vertical line is the true input value of that parameter in the DES data vector (which does not necessarily coincide with the parameter values preferred by the external data). The vertical shaded bands show the marginalized 68% CL constraints in the baseline model for the DES-only synthetic data (blue) and DES+external. The horizontal error bars show the inferred constraint for each individual addition to the synthetic data vector which are listed in rows; they match the shaded bands for the baseline case. For subsequent rows, they show the inferred constraint for each individual addition to the synthetic data vector as listed on the right. Some cases that appear inconsistent with the baseline analysis are discussed further in Sec. \ref{['sec:valid_sim']}. In cases where the prior is informative, we also include a dashed vertical line to signify the prior edge.
• Figure 3: Posterior constraints on the spatial curvature (left panel) and the number of relativistic species (right panel) in two of the extensions to $\Lambda$CDM considered in this paper. Blue contours show DES alone, yellow is external data alone, and red is the combination of the two. The 68% confidence region is shaded. The x-axis ranges in both panels coincide with the priors given to $\Omega_k$ and $N_{\mathrm{eff}}$, respectively. Posteriors' maxima are normalized to unity for better visibility of the DES only results.
• Figure 4: Constraints on dark energy parameters $(w_0, w_a)$ (left panel) and the modified gravity parameters $(\Sigma_0, \mu_0)$ (right panel). Blue contours show the 68% and 95% confidence regions from DES alone, yellow is external data alone, and red is the combination of the two. The intersection of the horizontal and vertical dashed lines shows the parameter values in the $\Lambda$CDM model (left panel) and in general relativity (right). The x-axis range in the left panel and the y-axis range in the right panel coincide with the respective priors given to $w_0$ and $\mu_0$. The cause of the nonintuitive shift in the combined $\Sigma_0$ constraint (red contour) relative to separate constraints is discussed in Sec. \ref{['sec:results']}.
• Figure 5: Constraints on the pivot value of the dark energy equation-of-state $w_p$ and the variation with scale factor $w_a$ Blue contours show DES alone, yellow is external data alone, and red is the combination of the two. The intersection of the horizontal and vertical dashed lines shows the parameter values in the $\Lambda$CDM model.