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

TL;DR

DES Year 1 presents a high-precision, multi-probe cosmological analysis combining galaxy clustering, galaxy-galaxy lensing, and cosmic shear to constrain ΛCDM and wCDM. The study employs blinded pipelines, independent shape measurements, and a comprehensive parameter set with 20 nuisance terms, utilizing a 457×457 analytic covariance and nonlinear power spectra. The three two-point functions yield competitive Ω_m and S_8 constraints, show consistency with Planck when combined with BAO and SNe, and provide meaningful bounds on w and Σmν, highlighting the power of joint optical surveys to test structure growth across cosmic time. The results underscore the coherence of late-time structure with early-Universe physics and establish a foundation for the significantly larger DES data set (DES Y3) to further refine dark energy and neutrino properties.

Abstract

We present cosmological results from a combined analysis of galaxy clustering and weak gravitational lensing, using 1321 deg$^2$ of $griz$ imaging data from the first year of the Dark Energy Survey (DES Y1). We combine three two-point functions: (i) the cosmic shear correlation function of 26 million source galaxies in four redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. To demonstrate the robustness of these results, we use independent pairs of galaxy shape, photometric redshift estimation and validation, and likelihood analysis pipelines. To prevent confirmation bias, the bulk of the analysis was carried out while blind to the true results; we describe an extensive suite of systematics checks performed and passed during this blinded phase. The data are modeled in flat $Λ$CDM and $w$CDM cosmologies, marginalizing over 20 nuisance parameters, varying 6 (for $Λ$CDM) or 7 (for $w$CDM) cosmological parameters including the neutrino mass density and including the 457 $\times$ 457 element analytic covariance matrix. We find consistent cosmological results from these three two-point functions, and from their combination obtain $S_8 \equiv σ_8 (Ω_m/0.3)^{0.5} = 0.783^{+0.021}_{-0.025}$ and $Ω_m = 0.264^{+0.032}_{-0.019}$ for $Λ$CDM for $w$CDM, we find $S_8 = 0.794^{+0.029}_{-0.027}$, $Ω_m = 0.279^{+0.043}_{-0.022}$, and $w=-0.80^{+0.20}_{-0.22}$ at 68% CL. The precision of these DES Y1 results rivals that from the Planck cosmic microwave background measurements, allowing a comparison of structure in the very early and late Universe on equal terms. Although the DES Y1 best-fit values for $S_8$ and $Ω_m$ are lower than the central values from Planck ...

Figures (22)

• Figure 1: Estimated redshift distributions of the lens and source galaxies used in the Y1 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). Note that source galaxies are chosen via two different pipelines im3shape and metacalibration, so their redshift distributions and total numbers differ (solid vs. dashed lines).
• Figure 2: Top panels: scaled angular correlation function, $\theta w(\theta)$, of redMaGiC galaxies in the five redshift bins in the top panel of Figure \ref{['fig:plot_nofzs']}, from lowest (left) to highest redshift (right) wthetapaper. The solid lines are predictions from the $\Lambda$CDM model that provides the best fit to the combined three two-point functions presented in this paper. Bottom panels: scaled galaxy--galaxy lensing signal, $\theta \gamma_t$ (galaxy-shear correlation), measured in DES Y1 in four source redshift bins induced by lens galaxies in five redMaGiC bins gglpaper. Columns represent different lens redshift bins while rows represent different source redshift bins, so e.g., bin labeled 12 is the signal from the galaxies in the second source bin lensed by those in the first lens bin. The solid curves are again our best-fit $\Lambda$CDM prediction. In all panels, shaded areas display the angular scales that have been excluded from our cosmological analysis (see §\ref{['sec:method']}).
• Figure 3: The cosmic shear correlation functions $\xi_+$ (top panel) and $\xi_-$ (bottom panel) in DES Y1 in four source redshift bins, including cross correlations, measured from the metacalibration shear pipeline (see shearcorr for the corresponding plot with im3shape); pairs of numbers in the upper left of each panel indicate the redshift bins. The solid lines show predictions from our best-fit $\Lambda$CDM model from the analysis of all three two-point functions, and the shaded areas display the angular scales that are not used in our cosmological analysis (see §\ref{['sec:method']}).
• Figure 4: Histogram of the differences between the best-fit $\Lambda$CDM model predictions and the 457 data points shown in Figures \ref{['fig:wgt']} and \ref{['fig:xipm']}, in units of the standard deviation of the individual data points. Although the covariance matrix is not diagonal, and thus the diagonal error bars do not tell the whole story, it is clear that there are no large outliers that drive the fits.
• Figure 5: $\Lambda$CDM constraints from DES Y1 on $\Omega_m, \sigma_8$, and $S_8$ from cosmic shear (green), redMaGiC galaxy clustering plus galaxy--galaxy lensing (red), and their combination (blue). Here, and in all such 2D plots below, the two sets of contours depict the 68% and 95% confidence levels.