Measuring cluster peculiar velocities with the Sunyaev-Zeldovich effects: scaling relations and systematics

The fluctuations in the Cosmic Microwave Background (CMB) intensity due to the Sunyaev-Zeldovich (SZ) effect are the sum of a thermal and a kinetic contribution. Separating the two components to measure the peculiar velocity of galaxy clusters requires radio and microwave observations at three or more frequencies, and knowledge of the temperature T_e of the intracluster medium weighted by the electron number density. To quantify the systematics of this procedure, we extract a sample of 117 massive clusters at redshift z=0 from an N-body hydrodynamical simulation, with 2x480^3 particles, of a cosmological volume 192 Mpc/h on a side of a flat Cold Dark Matter model with Omega_0=0.3 and Lambda=0.7. Our simulation includes radiative cooling, star formation and the effect of feedback and galactic winds from supernovae. We find that (1) our simulated clusters reproduce the observed scaling relations between X-ray and SZ properties; (2) bulk flows internal to the intracluster medium affect the velocity estimate by less than 200 km/s in 93 per cent of the cases; (3) using the X-ray emission weighted temperature, as an estimate of T_e, can overestimate the peculiar velocity by 20-50 per cent, if the microwave observations do not spatially resolve the cluster. For spatially resolved clusters, the assumptions on the spatial distribution of the ICM, required to separate the two SZ components, still produce a velocity overestimate of 10-20 per cent, even with an unbiased measure of T_e. Thanks to the large size of our cluster samples, these results set a robust lower limit of 200 km/s to the systematic errors that will affect upcoming measures of cluster peculiar velocities with the SZ effect.Comment: 14 pages, 12 figures, MNRAS, in press. Figures 3 and 4 now contain more recent observational data. Other minor revisions according to referee's comment

Dark Energy Survey year 1 results: Joint analysis of galaxy clustering, galaxy lensing, and CMB lensing two-point functions

We perform a joint analysis of the auto and cross-correlations between three cosmic fields: the galaxy density field, the galaxy weak lensing shear field, and the cosmic microwave background (CMB) weak lensing convergence field. These three fields are measured using roughly 1300 sq. deg. of overlapping optical imaging data from first year observations of the Dark Energy Survey and millimeter-wave observations of the CMB from both the South Pole Telescope Sunyaev-Zel'dovich survey and Planck. We present cosmological constraints from the joint analysis of the two-point correlation functions between galaxy density and galaxy shear with CMB lensing. We test for consistency between these measurements and the DES-only two-point function measurements, finding no evidence for inconsistency in the context of flat $\Lambda$CDM cosmological models. Performing a joint analysis of five of the possible correlation functions between these fields (excluding only the CMB lensing autospectrum) yields $S_{8}\equiv \sigma_8\sqrt{\Omega_{\rm m}/0.3} = 0.782^{+0.019}_{-0.025}$ and $\Omega_{\rm m}=0.260^{+0.029}_{-0.019}$. We test for consistency between these five correlation function measurements and the Planck-only measurement of the CMB lensing autospectrum, again finding no evidence for inconsistency in the context of flat $\Lambda$CDM models. Combining constraints from all six two-point functions yields $S_{8}=0.776^{+0.014}_{-0.021}$ and $\Omega_{\rm m}= 0.271^{+0.022}_{-0.016}$. These results provide a powerful test and confirmation of the results from the first year DES joint-probes analysis

Cosmological lensing ratios with des Y1, SPT, and Planck

Correlations between tracers of the matter density field and gravitational lensing are sensitive to the evolution of the matter power spectrum and the expansion rate across cosmic time. Appropriately defined ratios of such correlation functions, on the other hand, depend only on the angular diameter distances to the tracer objects and to the gravitational lensing source planes. Because of their simple cosmological dependence, such ratios can exploit available signal-to-noise ratio down to small angular scales, even where directly modelling the correlation functions is difficult. We present a measurement of lensing ratios using galaxy position and lensing data from the Dark Energy Survey, and CMB lensing data from the South Pole Telescope and Planck, obtaining the highest precision lensing ratio measurements to date. Relative to the concordance CDM model, we find a best-fitting lensing ratio amplitude of A = 1.1 ± 0.1. We use the ratio measurements to generate cosmological constraints, focusing on the curvature parameter. We demonstrate that photometrically selected galaxies can be used to measure lensing ratios, and argue that future lensing ratio measurements with data from a combination of LSST and Stage-4 CMB experiments can be used to place interesting cosmological constraints, even after considering the systematic uncertainties associated with photometric redshift and galaxy shear estimation

Dark Energy Survey Year 1 Results: Tomographic cross-correlations between Dark Energy Survey galaxies and CMB lensing from South Pole Telescope+Planck

We measure the cross-correlation between redMaGiC galaxies selected from the Dark Energy Survey (DES) year 1 data and gravitational lensing of the cosmic microwave background (CMB) reconstructed from South Pole Telescope (SPT) and Planck data over 1289 deg2. When combining measurements across multiple galaxy redshift bins spanning the redshift range of 0.1

CMB lensing tomography with the DES Science Verification galaxies

We measure the cross-correlation between the galaxy density in the Dark Energy Survey (DES) Science Verification data and the lensing of the cosmic microwave background (CMB) as reconstructed with the Planck satellite and the South Pole Telescope (SPT). When using the DES main galaxy sample over the full redshift range 0.2 2sigma) detections in all bins. Comparing to the fiducial Planck cosmology, we find the redshift evolution of the signal matches expectations, although the amplitude is consistently lower than predicted across redshift bins. We test for possible systematics that could affect our result and find no evidence for significant contamination. Finally, we demonstrate how these measurements can be used to constrain the growth of structure across cosmic time. We find the data are fit by a model in which the amplitude of structure in the z< 1.2 universe is 0.73 ± 0.16 times as large as predicted in the Lambda cold dark matter Planck cosmology, a 1.7sigma deviation

Optical–SZE scaling relations for DES optically selected clusters within the SPT-SZ survey

We study the Sunyaev–Zel'dovich effect (SZE) signature in South Pole Telescope (SPT) data for an ensemble of 719 optically identified galaxy clusters selected from 124.6 deg² of the Dark Energy Survey (DES) science verification data, detecting a clear stacked SZE signal down to richness λ ∼ 20. The SZE signature is measured using matched-filtered maps of the 2500 deg2 SPT-SZ survey at the positions of the DES clusters, and the degeneracy between SZE observable and matched-filter size is broken by adopting as priors SZE and optical mass–observable relations that are either calibrated using SPT-selected clusters or through the Arnaud et al. (A10) X-ray analysis. We measure the SPT signal-to-noise ζ–λ relation and two integrated Compton-yY500–λ relations for the DES-selected clusters and compare these to model expectations that account for the SZE–optical centre offset distribution. For clusters with λ > 80, the two SPT-calibrated scaling relations are consistent with the measurements, while for the A10-calibrated relation the measured SZE signal is smaller by a factor of 0.61 ± 0.12 compared to the prediction. For clusters at 20 < λ < 80, the measured SZE signal is smaller by a factor of ∼0.20–0.80 (between 2.3σ and 10σ significance) compared to the prediction, with the SPT-calibrated scaling relations and larger λ clusters showing generally better agreement. We quantify the required corrections to achieve consistency, showing that there is a richness-dependent bias that can be explained by some combination of (1) contamination of the observables and (2) biases in the estimated halo masses. We also discuss particular physical effects associated with these biases, such as contamination of λ from line-of-sight projections or of the SZE observables from point sources, larger offsets in the SZE-optical centring or larger intrinsic scatter in the λ–mass relation at lower richnesses

Mass calibration of optically selected DES clusters using a measurement of CMB-cluster lensing with SPTpol data

We use cosmic microwave background (CMB) temperature maps from the 500 deg2 SPTpol survey to measure the stacked lensing convergence of galaxy clusters from the Dark Energy Survey (DES) Year-3 redMaPPer (RM) cluster catalog. The lensing signal is extracted through a modified quadratic estimator designed to be unbiased by the thermal Sunyaev-Zel{'}dovich (tSZ) effect. The modified estimator uses a tSZ-free map, constructed from the SPTpol 95 and 150 GHz datasets, to estimate the background CMB gradient. For lensing reconstruction, we employ two versions of the RM catalog: a flux-limited sample containing 4003 clusters and a volume-limited sample with 1741 clusters. We detect lensing at a significance of 8.7 σ (6.7σ) with the flux(volume)-limited sample. By modeling the reconstructed convergence using the Navarro-Frenk-White profile, we find the average lensing masses to be M200m = (1.62 +0.32 −0.25 [stat.] ± 0.04 [sys.]) and (1.28 +0.14 −0.18 [stat.] ±0.03 [sys.])×1014 M⊙for the volume- and flux-limited samples respectively. The systematic error budget is much smaller than the statistical uncertainty and is dominated by the uncertainties in the RM cluster centroids. We use the volume-limited sample to calibrate the normalization of the mass-richness scaling relation, and find a result consistent with the galaxy weak-lensing measurements from DES (Mcclintock et al. 2018)

Numerical optimisation of mechanical ring reinforcement for bulk high-Temperature superconductors

Abstract The finite element method has been used extensively in recent years to solve various problems related to applied superconductivity and provides a useful tool for analysing and predicting experimental results. Based on a recently-developed modelling framework, implemented in the finite element software package COMSOL Multiphysics, investigations on the minimum ring reinforcement required to prevent mechanical failure in bulk high-temperature superconducting magnets have been carried out. Assuming homogeneous Jc (B,T) across the bulk sample irrespective of its dimensions, the maximum magnetic stresses experienced, and the minimum ring thickness required to prevent the hoop and radial stresses from exceeding the tensile strength of the bulk superconductor have been determined for varying values of the Young’s modulus, radius, height and temperature of a representative single-grain Ag-containing Gd-Ba-Cu-O bulk sample. This comprehensive analysis details the influence each of these key parameters has on the magnetic stress and hence their impact on the necessary ring thickness to prevent mechanical failure in any given system, i.e., for any combination of material properties and sample dimensions.</jats:p

Dark Energy Survey Year 1 Results: Cross-correlation between Dark Energy Survey Y1 galaxy weak lensing and South Pole Telescope +Planck CMB weak lensing

We cross-correlate galaxy weak lensing measurements from the Dark Energy Survey (DES) year-one data with a cosmic microwave background (CMB) weak lensing map derived from South Pole Telescope (SPT) and Planck data, with an effective overlapping area of 1289 deg2. With the combined measurements from four source galaxy redshift bins, we obtain a detection significance of 5.8σ. We fit the amplitude of the correlation functions while fixing the cosmological parameters to a fiducial ΛCDM model, finding A=0.99±0.17. We additionally use the correlation function measurements to constrain shear calibration bias, obtaining constraints that are consistent with previous DES analyses. Finally, when performing a cosmological analysis under the ΛCDM model, we obtain the marginalized constraints of ωm=0.261-0.051+0.070 and S8σ8ωm/0.3=0.660-0.100+0.085. These measurements are used in a companion work that presents cosmological constraints from the joint analysis of two-point functions among galaxies, galaxy shears, and CMB lensing using DES, SPT, and Planck data

A measurement of CMB cluster lensing with SPT and DES year 1 data

Clusters of galaxies gravitationally lens the cosmic microwave background (CMB) radiation, resulting in a distinct imprint in the CMB on arcminute scales. Measurement of this effect offers a promising way to constrain the masses of galaxy clusters, particularly those at high redshift. We use CMB maps from the South Pole Telescope Sunyaev–Zel’dovich (SZ) survey to measure the CMB lensing signal around galaxy clusters identified in optical imaging from first year observations of the Dark Energy Survey. The cluster catalogue used in this analysis contains 3697 members with mean redshift of z¯ = 0.45. We detect lensing of the CMB by the galaxy clusters at 8.1σ significance. Using the measured lensing signal, we constrain the amplitude of the relation between cluster mass and optical richness to roughly 17 per cent precision, finding good agreement with recent constraints obtained with galaxy lensing. The error budget is dominated by statistical noise but includes significant contributions from systematic biases due to the thermal SZ effect and cluster miscentring