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Dark Energy Survey Year 1 Results: Cosmological Constraints from Cosmic Shear

M. A. Troxel, N. MacCrann, J. Zuntz, T. F. Eifler, E. Krause, S. Dodelson, D. Gruen, J. Blazek, O. Friedrich, S. Samuroff, J. Prat, L. F. Secco, C. Davis, A. Ferté, J. DeRose, A. Alarcon, A. Amara, E. Baxter, M. R. Becker, G. M. Bernstein, S. L. Bridle, R. Cawthon, C. Chang, A. Choi, J. De Vicente, A. Drlica-Wagner, J. Elvin-Poole, J. Frieman, M. Gatti, W. G. Hartley, K. Honscheid, B. Hoyle, E. M. Huff, D. Huterer, B. Jain, M. Jarvis, T. Kacprzak, D. Kirk, N. Kokron, C. Krawiec, O. Lahav, A. R. Liddle, J. Peacock, M. M. Rau, A. Refregier, R. P. Rollins, E. Rozo, E. S. Rykoff, C. Sánchez, I. Sevilla-Noarbe, E. Sheldon, A. Stebbins, T. N. Varga, P. Vielzeuf, M. Wang, R. H. Wechsler, B. Yanny, T. M. C. Abbott, F. B. Abdalla, S. Allam, J. Annis, K. Bechtol, A. Benoit-Lévy, E. Bertin, D. Brooks, E. Buckley-Geer, D. L. Burke, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, F. J. Castander, M. Crocce, C. E. Cunha, C. B. D'Andrea, L. N. da Costa, D. L. DePoy, S. Desai, H. T. Diehl, J. P. Dietrich, P. Doel, E. Fernandez, B. Flaugher, P. Fosalba, J. García-Bellido, E. Gaztanaga, D. W. Gerdes, T. Giannantonio, D. A. Goldstein, R. A. Gruendl, J. Gschwend, G. Gutierrez, D. J. James, T. Jeltema, M. W. G. Johnson, M. D. Johnson, S. Kent, K. Kuehn, S. Kuhlmann, N. Kuropatkin, T. S. Li, M. Lima, H. Lin, M. A. G. Maia, M. March, J. L. Marshall, P. Martini, P. Melchior, F. Menanteau, R. Miquel, J. J. Mohr, E. Neilsen, R. C. Nichol, B. Nord, D. Petravick, A. A. Plazas, A. K. Romer, A. Roodman, M. Sako, E. Sanchez, V. Scarpine, R. Schindler, M. Schubnell, M. Smith, R. C. Smith, M. Soares-Santos, F. Sobreira, E. Suchyta, M. E. C. Swanson, G. Tarle, D. Thomas, D. L. Tucker, V. Vikram, A. R. Walker, J. Weller, Y. Zhang

TL;DR

The paper presents the most significant cosmic shear measurement from DES Year 1, constraining ΛCDM and wCDM with a varying neutrino mass and using two independent shape catalogs and photo-z calibrations. It employs extensive simulations (Buzzard, MICE-GC, FLASK lognormal) and a halo-model covariance, with rigorous blinding and robustness tests across shear pipelines, IA models, and photo-z systematics. The results yield S_8 = 0.782 ± 0.027 in ΛCDM and S_8 = 0.777 ± 0.036–0.038, w = -0.95^{+0.33}_{-0.39} in wCDM, finding no strong evidence for w ≠ -1 and good concordance with Planck and KiDS data. The study also demonstrates resilience to modeling choices and paves the way for substantial gains with future DES data and joint analyses combining weak lensing with clustering and galaxy-galaxy lensing.

Abstract

We use 26 million galaxies from the Dark Energy Survey (DES) Year 1 shape catalogs over 1321 deg$^2$ of the sky to produce the most significant measurement of cosmic shear in a galaxy survey to date. We constrain cosmological parameters in both the flat $Λ$CDM and $w$CDM models, while also varying the neutrino mass density. These results are shown to be robust using two independent shape catalogs, two independent \photoz\ calibration methods, and two independent analysis pipelines in a blind analysis. We find a 3.5\% fractional uncertainty on $σ_8(Ω_m/0.3)^{0.5} = 0.782^{+0.027}_{-0.027}$ at 68\% CL, which is a factor of 2.5 improvement over the fractional constraining power of our DES Science Verification results. In $w$CDM, we find a 4.8\% fractional uncertainty on $σ_8(Ω_m/0.3)^{0.5} = 0.777^{+0.036}_{-0.038}$ and a dark energy equation-of-state $w=-0.95^{+0.33}_{-0.39}$. We find results that are consistent with previous cosmic shear constraints in $σ_8$ -- $Ω_m$, and see no evidence for disagreement of our weak lensing data with data from the CMB. Finally, we find no evidence preferring a $w$CDM model allowing $w\ne -1$. We expect further significant improvements with subsequent years of DES data, which will more than triple the sky coverage of our shape catalogs and double the effective integrated exposure time per galaxy.

Dark Energy Survey Year 1 Results: Cosmological Constraints from Cosmic Shear

TL;DR

The paper presents the most significant cosmic shear measurement from DES Year 1, constraining ΛCDM and wCDM with a varying neutrino mass and using two independent shape catalogs and photo-z calibrations. It employs extensive simulations (Buzzard, MICE-GC, FLASK lognormal) and a halo-model covariance, with rigorous blinding and robustness tests across shear pipelines, IA models, and photo-z systematics. The results yield S_8 = 0.782 ± 0.027 in ΛCDM and S_8 = 0.777 ± 0.036–0.038, w = -0.95^{+0.33}_{-0.39} in wCDM, finding no strong evidence for w ≠ -1 and good concordance with Planck and KiDS data. The study also demonstrates resilience to modeling choices and paves the way for substantial gains with future DES data and joint analyses combining weak lensing with clustering and galaxy-galaxy lensing.

Abstract

We use 26 million galaxies from the Dark Energy Survey (DES) Year 1 shape catalogs over 1321 deg of the sky to produce the most significant measurement of cosmic shear in a galaxy survey to date. We constrain cosmological parameters in both the flat CDM and CDM models, while also varying the neutrino mass density. These results are shown to be robust using two independent shape catalogs, two independent \photoz\ calibration methods, and two independent analysis pipelines in a blind analysis. We find a 3.5\% fractional uncertainty on at 68\% CL, which is a factor of 2.5 improvement over the fractional constraining power of our DES Science Verification results. In CDM, we find a 4.8\% fractional uncertainty on and a dark energy equation-of-state . We find results that are consistent with previous cosmic shear constraints in -- , and see no evidence for disagreement of our weak lensing data with data from the CMB. Finally, we find no evidence preferring a CDM model allowing . We expect further significant improvements with subsequent years of DES data, which will more than triple the sky coverage of our shape catalogs and double the effective integrated exposure time per galaxy.

Paper Structure

This paper contains 36 sections, 19 equations, 19 figures, 6 tables.

Table of Contents

  1. Introduction
  2. Dark Energy Survey Year 1 Data
  3. Shape Catalogs
  4. Metacalibration
  5. im3shape
  6. Photometric Redshift Estimates
  7. Simulations and Mock Catalogs
  8. Buzzard Mock Catalogs
  9. MICE-GC Mock Catalogs
  10. Lognormal Mock Catalogs
  11. Cosmic Shear Measurement
  12. Covariance Matrix
  13. Blinding
  14. Modeling Choices
  15. Matter Power Spectrum Modeling and Baryonic Effects
  16. ...and 21 more sections

Figures (19)

  • Figure 1: The footprint of the DES Y1 Metacalibration catalog selection used in this work, covering 1321 deg$^2$. The joint redMaGiC mask described in Sec. \ref{['sec:shapes']} is not included. The raw mean number density of objects drawn by Skymapper in HEALPix cells of $N_{\mathrm{side}}$ 1024 is shown, which is uncorrected for the coverage fraction at subpixel scales. Overlaid are the bounds of the nominal five year DES survey footprint. The full shape catalog footprint, which includes the 'Stripe 82' region, is shown in shearcat. For the Metacalibration catalog, $n_g$ is equivalent to the H12 $n_{\mathrm{eff}}$ in Table \ref{['table:neff']}.
  • Figure 2: The measured BPZ and resampled COSMOS redshift distributions for the Metacalibration shape catalog, binned by the means of the photo-$z$ posteriors into the four tomographic ranges in Table \ref{['table:neff']} and marked by the color shading. The normalization of each bin reflects their relative $n_{\textrm{eff}}$. The BPZ distributions are corrected by the mean of the redshift bias priors $\Delta z^i$. The contribution of each galaxy is weighted by $W_i S_i$, as defined in Sec. \ref{['sec:2pt']}. The im3shape redshift distributions are similar to those shown for Metacalibration. The second bin is clearly most different between the resampled COSMOS estimate and BPZ -- we explore this further in Sec. \ref{['sec:sysphotoz']} and show that it does not significantly impact the inferred cosmological parameters.
  • Figure 3: The measured non-tomographic shear correlation function $\xi_{\pm}$ for the DES Y1 shape catalogs. The best-fit $\Lambda$CDM theory line from the fiducial tomographic analysis is shown as the same solid line compared to measurements from both catalogs.
  • Figure 4: The measured shear correlation function $\xi_{+}$ (top triangle) and $\xi_{-}$ (bottom triangle) for the DES Y1 Metacalibration catalog. Results are scaled by the angular separation ($\theta$) to emphasize features and differences relative to the best-fit model. The correlation functions are measured in four tomographic bins spanning the redshift ranges listed in Table \ref{['table:neff']}, with labels for each bin combination in the upper left corner of each panel. The assignment of galaxies to tomographic bins is discussed in Sec. \ref{['sec:photoz']}. Scales which are not used in the fiducial analysis are shaded (see Sec. \ref{['sec:systheory']}). The best-fit $\Lambda$CDM theory line from the full tomographic analysis is shown as the solid line. We find a $\chi^2$ of 227 for 211 degrees of freedom in the non-shaded regions.
  • Figure 5: The measured shear correlation function $\xi_{+}$ (top triangle) and $\xi_{-}$ (bottom triangle) for the DES Y1 im3shape catalog (see caption of Fig. \ref{['fig:ximcal']}). The uncertainty on $\xi_{\pm}$ is clearly larger for im3shape compared to Metacalibration in Fig. \ref{['fig:ximcal']} due to the lower number density of objects. We find a $\chi^2$ of 224 for 211 degrees of freedom in the non-shaded regions.
  • ...and 14 more figures