1708.01441
Weak lensing deflection of three-point correlation functions
Pyne, Joachimi, Peiris
WL alters the apparent separations between observed sources, potentially affecting clustering statistics. Derive a general expression for the lensing deflection which is valid for any 3-pt statistic, and investigate its effect on the 3pt clustering correlation function. Find that deflection of the clustering correction function is greatest at around z=2. It is most prominent in regions where the correlation function varies rapidly, in particular at the baryon acoustic oscillation scale where it smooths out the peaks and troughs, reducing the peak-to-trough difference by about 0.1 percent at z=1 and around 2.3 percent at z=10. The modification due to lensing defection is typically at the per cent level of the expected errors in a euclid-like survey and therefore undetectable.
1708.01530
Dark Energy Survey Year 1 Results: cosmological constraints from galaxy clustering and weak lensing
DES Collaboration
Present cosmological results from a combined analysis of galaxy clustering and WL, using 1321 deg^2 of griz imaging data from DES Y1. Combine three 2pt functions: (i) the cosmic shear correlation function of 16 million source galaxies in 4 redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 LRGs in 5 z bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. To demonstrate the robustness of these results, use independent pairs of galaxy shape, photometric z 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; describe an extensive suite of systematics checks performed and passed during this blinded phase. The data are modeled in flat LCDM and wCDM cosmologies, marginalizing over 20 nuisance parameters, varying 6 (for LCDM) or 7 (for wCDM) cosmological parameters including the neutrino mass density and including the 457x457 element analytic covariance matrix. Find consistent cosmological results from these 3 two-point functions, and from their combination obtain S8=sigma8(Omega_m/0.3)^0.5=0.783±0.02 and Omega_m=0.264+0.03-0.02 for LCDM. For wCDM, find S8=0.794±0.02 and Omega_m=0.279+0.04-0.02, and w=-0.80±0.2 at 68% CL. The precision of these DES Y1 results rivals that from the Planck CMB measurements, allowing a comparison of structure in the very early and late Universe on equal terms. Although the DES Y1 best-fit values for S8 and Omega_m are lower than the central values from Planck for both LCDM and wCDM, the Bayes factor indicates that the DES Y1 and Planck data sets are consistent with each other in the context of LCDM. Combining DES Y1 with Planck, BAO measurements from SDSS, 6dF, and BOSS, and SNe Ia from the JLA dataset, derive very tight constraints on cosmological parameters: S8=0.799±0.01 and Omega_m = 0.301±0.008 in LCDM, and w=-1.00±0.05 in wCDM. Upcoming DES analyses will provide more stringent test of the LCDM model and extensions such as time-varying equation of state of DE or modified gravity.
1708.01531
Dark Energy Survey Year 1 results: photometric data set for cosmology
Drlica-Wagner, et al
DES internal Y1A1 GOLD cosmology dataset, from multiple epochs of DES imaging, consisting of calibrated photometric zeropointes, object catalogs, and ancillary data products (maps of survey depth and observing conditions, star-galaxy classification, and photo-z estimates) that are necessary for accuracy cosmo analyses. Consists of ~137 million objects over ~1800 deg^2 in DES grizY filters. 10 sigma limiting mag for galaxies is g=23.4, r=23.2, i=22.5, z=21.8, and Y=20.1. Photometric calibration by stellar-locus regression, with absolute calibration accuracy better than 2% over the survey area. Enables measurements of cosmic acceleration at z<~1.
1708.01532
Dark Energy Survey Year 1 results: Redshift distributions of the weak lensing source galaxies
Hoyle, Gruen, Bernstein, et al
Describe the derivation and validation of z distribution estimates and their uncertainties for the galaxies used as WL sources in DES Y1 cosmo analyses. BPZ code is used to assign galaxies to 4 z bins between z=0.2 and 1.3, and to produce initial estimates of the lensing-weighted z distributions n_PZ^i(z) for bin i. Accurate determination of cosmo parameters depends critically on knowledge of n^i but is insensitive to bin assignments or z errors for individual galaxies. The cosmological analyses allow for shifts n^i(z)=n^i_PZ(z-Delta z^i) to correct the mean redshift of n^i(z) for biases in n^i_PZ. The Delta z^i are constrained by comparison of independently estimated 30-band photo-z of galaxies in the COSMOS field to BPZ estimates made from the DES griz fluxes, for a sample matched in fluxes, pre-seeing size, and lensing weight to the DES WL sources. In companion papers, the Delta z^i are further constrained by the angular clustering of the source galaxies around red galaxies with secure photo-z at 0.15<z<0.9. This paper details the BPZ and COSMOS procedures, and demonstrates that the cosmological inference is insensitive to details of the n^i(z) beyond the choice of Delta z^i. The clustering and COSMOS validation methods produce consistent estimates of Delta z^i, with combined uncertainties of sigma_Delta z^i=0.015, 0.013, 0.011, and 0.022 in the 4 bins. Marginalize over these in all analyses to follow, which does not diminish the constraining power significantly. Repeating the photo-z procedure using the Directional Neighborhood Fitting (DNF) algorithm instead of BPZ, or using the n^i(z) directly estimated from COSMOS, yields no discernible difference in cosmological inferences.
1708.01533
Dark Energy Survey Year 1 results: Weak lensing shape catalogues
Zuntz, Sheldon, et al
1708.01534
Dark Energy Survey Year 1 results: The impact of galaxy neighbors on weak lensing cosmology with im3shape
Samuroff, Bridle, Zuntz, et al
Use a suite of simulated images based on DES Y1 to explore the impact of galaxy neighbors on shape measurement and shear cosmology. The hoopoe image sims include realistic blending, galaxy positions, and spatial variations in depth and PSF properties. Using the im3shape maximum-likelihood shape measurement code, identify 4 mechanisms by which neighbors can have a non-negligible influence on shear estimation. These effects, if ignored, would contribute a net multiplicative bias of m~0.03-0.09 in the DES Y1 im3shape catalogue, though the precise impact will be dependent on both the measurement code and the selection cuts applied. This can be reduced to percentage level or less by removing objects with close neighbors, at a cost to the effective number density of galaxies n_eff of 30%. Use the cosmological inference pipeline of DES Y1 to explore the cosmo implications of neighbor bias and show that omitting blending from the calibration simulation for DES Y1 would bias the inferred clustering amplitude S8=sigma8(Omega_m/0.3)^0.5 by 2 sigma towards low values. Use the hoopoe sims to test the effect of neighbor-induced spatial correlations in the multiplicative bias. Find the impact on the recovered S8 of ignoring such correlations to be subdominant to statistical error at the current level of precision.
1708.01535
Dark Energy Survey Year 1 results: Curved-Sky weak lensing mass map
Chang, Pujol, et al
Construct the largest curved-sky galaxy WL mass map to date from DES Y1 data. The map, about 10x larger than previous work, is constructed over a contiguous ~1500 deg^2, covering a comoving volume of ~10 Gpc^3. The effects of masking, sampling and noise are tested using simulations. Generate WL maps from 2 DES Y1 shear catalogs, Metacalibration and Im3shape, with sources at 0.2<z<1.3, and in each of 4 bins in this range. In the highest S/N map, the ratio between the mean S/N in the E-mode and the B-mode map is ~1.5(~2) when smoothed with a Gaussian filter of sigma_G=30(80) arc minutes. The second and third moments of the convergence kappa in the maps are in agreement with sims. Also find no significant correlation of kappa with maps of potential systematic contaminants. Finally, demonstrate 2 applications of the mass maps: (1) cross-correlation with different foreground tracers of mass and (2) exploration of the largest peaks and voids in the maps.
1708.01536
Dark Energy Survey Year 1 results: Galaxy clustering for combined probes
Elvin-Poole, Crocce, Ross, et al
Measure the clustering of DES Y1 galaxies that are intended to be combined with WL samples in order to produce cosmo constraints from the joint analysis of LSS and lensing correlations. 2pt correlation functions are measured for a sample of 6.6e5 LRGs selected using the redMaGiC algorithm over an area of 1321 square degrees, in the range 0.15<z<0.9, split into 5 tomographic z bins. The sample has a mean redshift uncertainty of sigma_z/(1+z)=0.017. Quantify and correct spurious correlations induced by spatially variable survey properties, testing their impact on the clustering measurements and covariance. Demonstrate the sample's robustness by testing for stellar contamination, for potential biases that could arise for the systematic correction, and for the consistency between the 2pt auto- and cross-correlation functions. Show that the corrections applied have a significant impact on the resultant measurement of cosmo params, but that the results are robust against arbitrary choices in the correction method. Find the linear galaxy bias in each z bin in a fiducial cosmology to be b(z=0.24) =1.50±0.08, b(z=0.38)=1.61±0.05, b(z=0.53)=1.60±0.04 for galaxies with luminosities L/L* > 0.5, b(z=0.68)=1.93±0.05 for L/L*>1 and b(z=0.83)=1.99±0.07 for L/L*>1.5, broadly consistent with expectations for the z and L dependence of the bias of red galaxies. Show these measurements to be consistent with the linear bias obtained from tangential shear measurements.
1708.01537
Dark Energy Survey Year 1 results: Galaxy-galaxy lensing
Prat, et al
Present gg lensing measurements from 1321 deg^2 of DES Y1 data. The lens sample consists of a selection of 660,000 red galaxies with high-precision photo-z, known as redMaGiC, split into 5 tomographic bins in the range 0.15<z<0.9. Use 2 different source samples, obtained from Metacalibration (26M galaxies) and Im3shape (18M galaxies) shear estimation codes, which are split into 4 photo-z bins in the range 0.2<z<1.3. Perform extensive testing of potential systematic effects that can bias the gg lensing signal, including those from shear estimation, photo-z, and observational properties. Covariance are obtained from jackknife subsamples of the data and validated with a suite of log-normal simulations. Use the shear-ratio geometric test to obtain independent constraints on the mean of the source z distributions, providing validation of these obtained form other photo-z studies with the same data. Find consistency between the galaxy bias estimates obtained from the gg lensing measurements and from galaxy clustering, therefore showing the galaxy-matter cross-correlation coefficient r to be consistent with one, measured over the scales used for the cosmo analysis. The results in this work present one of the 3 2pt correlation functions, along with galaxy clustering and cosmic shear, used in the DES cosmo analysis of Y1 data, and hence the methodology and the systematics tests presented here provide a critical input for that study as well as for future cosmo analyses in DES and other photometric galaxy surveys.
1708.01538
Dark Energy Survey Year 1 results: Cosmological constraints from cosmic shear
Troxel, MacCrann, Zuntz, Eifler, Krause, Dodelson, Gruen, Blazek, et al
Use 26M galaxies from DES Y1 shape catalogs over 1321 deg^2 of the sky to produce the most significant measurement of cosmic shear in a galaxy survey to date. Constrain cosmological parameters in both the flat LCDM and wCDM models, while also varying the neutrino mass density. These results are shown to be robust using 2 independent shape catalogs, 2 independent photo-z calibration methods, and 2 independent analysis pipelines in a blind analysis. Find a 3% fractional uncertainty on sigma8(Omega_m/0.3)^0.5 = 0.789±0.025 at 68% CL, which is a factor of 3 improvement over the fractional constraining power of the DES SV results and a factor 1.5 tighter than the previous state-of-the-art cosmic shear results. In wCDM, find a 5% fractional uncertainty on sigma8(Omega_m/0.3)^0.5 = 0.789±0.037 and a DE EoS w=-0.82+0.26-0.48. Find results that are consistent with previous cosmic shear constraints in sigma8-Omega_m, nevertheless see no evidence for disagreement of WL data with data from the CMB. Finally, find no evidence preferring a wCDM model allowing w!=-1. Expect further significant improvements with subsequent years of DES data, which will more than 3x the sky coverage of the shape catalogs and double the effective integrated exposure time per galaxy.
1708.01617
Large Synoptic Survey Telescope Galaxies Science Roadmap
Robertson, et al
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