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Register a new userDark Energy Survey Year 1 Results: Calibration of Cluster Mis-centering in the redMaPPer Catalogs
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The center determination of a galaxy cluster from an optical cluster finding algorithm can be offset from theoretical prescriptions or $N$-body definitions of its host halo center. These offsets impact the recovered cluster statistics, affecting both richness measurements and the weak lensing shear profile around the clusters. This paper models the centering performance of the RM~cluster finding algorithm using archival X-ray observations of RM-selected clusters. Assuming the X-ray emission peaks as the fiducial halo centers, and through analyzing their offsets to the RM~centers, we find that $sim 75pm 8 %$ of the RM~clusters are well centered and the mis-centered offset follows a Gamma distribution in normalized, projected distance. These mis-centering offsets cause a systematic underestimation of cluster richness relative to the well-centered clusters, for which we propose a descriptive model. Our results enable the DES Y1 cluster cosmology analysis by characterizing the necessary corrections to both the weak lensing and richness abundance functions of the DES Y1 redMaPPer cluster catalog.
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We constrain the mass--richness scaling relation of redMaPPer galaxy clusters identified in the Dark Energy Survey Year 1 data using weak gravitational lensing. We split clusters into $4times3$ bins of richness $lambda$ and redshift $z$ for $lambdageq20$ and $0.2 leq z leq 0.65$ and measure the mean masses of these bins using their stacked weak lensing signal. By modeling the scaling relation as $langle M_{rm 200m}|lambda,zrangle = M_0 (lambda/40)^F ((1+z)/1.35)^G$, we constrain the normalization of the scaling relation at the 5.0 per cent level as $M_0 = [3.081 pm 0.075 ({rm stat}) pm 0.133 ({rm sys})] cdot 10^{14} {rm M}_odot$ at $lambda=40$ and $z=0.35$. The richness scaling index is constrained to be $F=1.356 pm 0.051 ({rm stat})pm 0.008 ({rm sys})$ and the redshift scaling index $G=-0.30pm 0.30 ({rm stat})pm 0.06 ({rm sys})$. These are the tightest measurements of the normalization and richness scaling index made to date. We use a semi-analytic covariance matrix to characterize the statistical errors in the recovered weak lensing profiles. Our analysis accounts for the following sources of systematic error: shear and photometric redshift errors, cluster miscentering, cluster member dilution of the source sample, systematic uncertainties in the modeling of the halo--mass correlation function, halo triaxiality, and projection effects. We discuss prospects for reducing this systematic error budget, which dominates the uncertainty on $M_0$. Our result is in excellent agreement with, but has significantly smaller uncertainties than, previous measurements in the literature, and augurs well for the power of the DES cluster survey as a tool for precision cosmology and upcoming galaxy surveys such as LSST, Euclid and WFIRST.
Using data collected by the Dark Energy Survey (DES), we report the detection of intracluster light (ICL) with $sim300$ galaxy clusters in the redshift range of 0.2-0.3. We design methods to mask detected galaxies and stars in the images and stack the cluster light profiles, while accounting for several systematic effects (sky subtraction, instrumental point-spread function, cluster selection effects and residual light in the ICL raw detection from background and cluster galaxies). The methods allow us to acquire high signal-to-noise measurements of the ICL and central galaxies (CGs), which we separate with radial cuts. The ICL appears as faint and diffuse light extending to at least 1 Mpc from the cluster center, reaching a surface brightness level of 30 mag arcsec$^{-2}$. The ICL and the cluster CG contribute to $44%pm17$% of the total cluster stellar luminosity within 1 Mpc. The ICL color is overall consistent with that of the cluster red sequence galaxies, but displays the trend of becoming bluer with increasing radius. The ICL demonstrates an interesting self-similarity feature -- for clusters in different richness ranges, their ICL radial profiles are similar after scaling with cluster $R_mathrm{200m}$, and the ICL brightness appears to be a good tracer of the cluster radial mass distribution. These analyses are based on the DES redMaPPer cluster sample identified in the first year of observations.
We present the weak lensing mass calibration of the stellar mass based $mu_{star}$ mass proxy for redMaPPer galaxy clusters in the Dark Energy Survey Year 1. For the first time we are able to perform a calibration of $mu_{star}$ at high redshifts, $z>0.33$. In a blinded analysis, we use $sim 6,000$ clusters split into 12 subsets spanning the ranges $0.1 leqslant z<0.65$ and $mu_{star}$ up to $sim 5.5 times 10^{13} M_{odot}$, and infer the average masses of these subsets through modelling of their stacked weak lensing signal. In our model we account for the following sources of systematic uncertainty: shear measurement and photometric redshift errors, miscentring, cluster-member contamination of the source sample, deviations from the NFW halo profile, halo triaxiality and projection effects. We use the inferred masses to estimate the joint mass--$mu_{star}$--$z$ scaling relation given by $langle M_{200c} | mu_{star},z rangle = M_0 (mu_{star}/5.16times 10^{12} mathrm{M_{odot}})^{F_{mu_{star}}} ((1+z)/1.35)^{G_z}$. We find $M_0= (1.14 pm 0.07) times 10^{14} mathrm{M_{odot}}$ with $F_{mu_{star}}= 0.76 pm 0.06$ and $G_z= -1.14 pm 0.37$. We discuss the use of $mu_{star}$ as a complementary mass proxy to the well-studied richness $lambda$ for: $i)$ exploring the regimes of low $z$, $lambda<20$ and high $lambda$, $z sim 1$; $ii)$ testing systematics such as projection effects for applications in cluster cosmology.
The calibration and validation of scientific analysis in simulations is a fundamental tool to ensure unbiased and robust results in observational cosmology. In particular, mock galaxy catalogs are a crucial resource to achieve these goals in the measurement of Baryon Acoustic Oscillations (BAO) in the clustering of galaxies. Here we present a set of 1952 galaxy mock catalogs designed to mimic the Dark Energy Survey (DES) Year 3 BAO sample over its full photometric redshift range $0.6 < z_{rm photo} < 1.1$. The mocks are based upon 488 ICE-COLA fast $N$-body simulations of full-sky light-cones and are created by populating halos with galaxies, using a hybrid Halo Occupation Distribution - Halo Abundance Matching model. This model has 10 free parameters, which are determined, for the first time, using an automatic likelihood minimization procedure. We also introduce a novel technique to assign photometric redshift for simulated galaxies, following a two-dimensional probability distribution with VIMOS Public Extragalactic Redshift Survey (VIPERS) data. The calibration was designed to match the observed abundance of galaxies as a function of photometric redshift, the distribution of photometric redshift errors, and the clustering amplitude on scales smaller than those used for BAO measurements. An exhaustive analysis is done to ensure that the mocks reproduce the input properties. Finally, mocks are tested by comparing the angular correlation function $w(theta)$, angular power spectrum $C_ell$ and projected clustering $xi_p(r_perp)$ to theoretical predictions and data. The success in reproducing accurately the photometric redshift uncertainties and the galaxy clustering as a function of redshift render this mock creation pipeline as a benchmark for future analyses of photometric galaxy surveys.
We present galaxy-galaxy lensing measurements from 1321 sq. deg. of the Dark Energy Survey (DES) Year 1 (Y1) data. The lens sample consists of a selection of 660,000 red galaxies with high-precision photometric redshifts, known as redMaGiC, split into five tomographic bins in the redshift range $0.15 < z < 0.9$. We use two different source samples, obtained from the Metacalibration (26 million galaxies) and Im3shape (18 million galaxies) shear estimation codes, which are split into four photometric redshift bins in the range $0.2 < z < 1.3$. We perform extensive testing of potential systematic effects that can bias the galaxy-galaxy lensing signal, including those from shear estimation, photometric redshifts, and observational properties. Covariances are obtained from jackknife subsamples of the data and validated with a suite of log-normal simulations. We use the shear-ratio geometric test to obtain independent constraints on the mean of the source redshift distributions, providing validation of those obtained from other photo-$z$ studies with the same data. We find consistency between the galaxy bias estimates obtained from our galaxy-galaxy 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 cosmological analysis. The results in this work present one of the three two-point correlation functions, along with galaxy clustering and cosmic shear, used in the DES cosmological 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 cosmological analyses in DES and other photometric galaxy surveys.
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