Shear Signal Research Articles

Spectroscopic Tomography: A First Weak-lensing Detection Using Spectroscopic Redshifts Only

Abstract We describe the first spectroscopic tomographic (spectrotomographic) weak-lensing measurement for a galaxy cluster based only on background galaxies with spectroscopically determined redshifts. We use the massive cluster A2029 to demonstrate the power of combining spectroscopy and lensing to obtain accurate masses and to overcome biases from contamination and photometric redshift errors. We detect the shear signal from the cluster at > 3.9σ significance. The shear signal scales with source redshift in a way that is consistent with the angular diameter distance ratio variation in a ΛCDM universe. Furthermore, the amplitude of the measured signal is consistent with the X-ray mass. Upcoming spectroscopic instruments such as the Prime Focus Spectrograph on Subaru will permit spectrotomographic weak-lensing measurements with a signal-to-noise ratio comparable with current photometric-redshift-based weak-lensing measurements for hundreds of galaxy clusters. Thus, spectrotomography may enable sensitive cosmological constraints that complement and are independent of other measurement techniques.

Cosmological consequences of intrinsic alignments supersample covariance

ABSTRACT We examine cosmological constraints from high-precision weak-lensing surveys including supersample covariance (SSC) due to the finite survey volume. Specifically, we focus on the contribution of beat coupling in the intrinsic alignments as a part of full cosmic shear signal under flat-sky approximation. The SSC-effect grows by going to lower redshift bin and indicates considerable footprint on the intermediate and high multipoles for cumulative signal-to-noise ratio (SNR). The SNR is reduced by $\approx 10{{\ \rm per\ cent}}$ as a consequence of including the intrinsic alignment SSC, for the full cosmic shear signal, depending on the amplitude of intrinsic alignments, the ellipticity dispersion, and the survey redshift ranges, while the contribution of photometric redshift error can be ignored in the cumulative SNR. Using the Fisher-matrix formalism, we find that the impact of large modes beyond the volume of the surveys on the small modes alters the intrinsic alignments. However, corresponding impact on the cosmological parameters’ estimation is marginal compared to that of for gravitational weak lensing, particularly, when all available redshift bins are considered. Our results also demonstrate that including SSC-effect on the intrinsic alignments in the analytical covariance matrix of full cosmic shear leads to increase marginally the confidence interval for σ8 by $\approx 10{{\ \rm per\ cent}}$ for a sample with almost high intrinsic alignment amplitude.

Mitigating Shear-dependent Object Detection Biases with Metacalibration

Abstract Metacalibration is a new technique for measuring weak gravitational lensing shear that is unbiased for isolated galaxy images. In this work we test metacalibration with overlapping, or “blended” galaxy images. Using standard metacalibration, we find a few percent shear measurement bias for galaxy densities relevant for current surveys, and that this bias increases with increasing galaxy number density. We show that this bias is not due to blending itself, but rather to shear-dependent object detection. If object detection is shear-independent, no deblending of images is needed, in principle. We demonstrate that detection biases are accurately removed when including object detection in the metacalibration process, a technique we call metadetection. This process involves applying an artificial shear to images of small regions of sky and performing detection on the sheared images, as well as measurements that are used to calculate a shear response. We demonstrate that the method can accurately recover weak shear signals even in highly blended scenes. In the metacalibration process, the space between objects is sheared coherently, which does not perfectly match the real universe in which some, but not all, galaxy images are sheared coherently. We find that even for the worst case scenario, in which the space between objects is completely unsheared, the resulting shear bias is at most a few tenths of a percent for future surveys. We discuss additional technical challenges that must be met in order to implement metadetection for real surveys.

The first shear measurements from precision weak lensing

ABSTRACT We present an end-to-end methodology to measure the effects of weak lensing on individual galaxy–galaxy systems exploiting their kinematic information. Using this methodology, we have measured a shear signal from the velocity fields of 18 weakly lensed galaxies. We selected a sample of systems based only on the properties of the sources, requiring them to be bright (apparent i-band magnitude <17.4) and in the nearby Universe ($z$ < 0.15). We have observed the velocity fields of the sources with WiFeS, an optical IFU on a 2.3 m telescope, and fitted them using a simple circular motion model with an external shear. We have measured an average shear of 〈γ〉 = 0.020 ± 0.008 compared to a predicted 〈γpred〉 = 0.005 obtained using median stellar-to-halo relationships from the literature. While still a statistical approach, our results suggest that this new weak lensing methodology can overcome some of the limitations of traditional stacking-based techniques. We describe in detail all the steps of the methodology and make publicly available all the velocity maps for the weakly lensed sources used in this study.

Source Distributions of Cosmic Shear Surveys in Efficiency Space

We show that the lensing efficiency of cosmic shear generically has a simple shape, even in the case of a tomographic survey with badly behaved photometric redshifts. We argue that source distributions for cosmic shear can therefore be more effectively parametrised in "efficiency space". Using realistic simulations, we find that the true lensing efficiency of a current cosmic shear survey without disconnected outliers in the redshift distributions can be described to per cent accuracy with only two parameters, and the approach straightforwardly generalises to other parametric forms and surveys. The cosmic shear signal is thus largely insensitive to the details of the source distributions, and the features that matter can be summarised by a small number of suitable efficiency parameters. For the simulated survey, we show that prior knowledge at the ten per cent level, which is attainable e.g. from photometric redshifts, is enough to marginalise over the efficiency parameters without severely affecting the constraints on the cosmology parameters Ω_m and σ₈. A Jupyter notebook and associated files can be found <a href="https://github.com/cosmiclens/arXiv-2003.11558">here</a>. <em>Open J. Astrophys. 3(2020) 6</em>

Brighter-fatter Effect in Near-infrared Detectors—III. Fourier-domain Treatment of Flat Field Correlations and Application to WFIRST

Weak gravitational lensing has emerged as a leading probe of the growth of cosmic structure. However, the shear signal is very small and accurate measurement depends critically on our ability to understand how non-ideal instrumental effects affect astronomical images. The Wide-Field Infrared Survey Telescope (WFIRST) will fly a focal plane containing 18 Teledyne H4RG-10 near-infrared detector arrays, which present different instrument calibration challenges from previous weak lensing observations. Previous work [Paper I: Hirata & Choi, PASP, 132, 014501 (2020); and Paper II: Choi & Hirata, PASP, 132, 014502 (2020)] has shown that correlation functions of flat field images, including cross-correlations between different time slices that are enabled by the non-destructive read capability of the infrared detectors, are effective tools for disentangling linear and nonlinear inter-pixel capacitance (IPC) and the brighter-fatter effect (BFE). Here we present a Fourier-domain treatment of the flat field correlations, which allows us to expand the previous formalism to all orders in IPC, BFE, and classical nonlinearity. We show that biases in simulated flat field analyses in Paper I are greatly reduced through the use of this formalism. We then apply this updated formalism to flat field data from three WFIRST flight candidate detectors, and explore the robustness to variations in the analysis. We find that the BFE is present in all three detectors, and that its contribution to the flat field correlations dominates over the nonlinear IPC, in accordance with the results from Paper II on a development detector. The magnitude of the BFE is such that the effective area of a pixel is increased by (3.54 ± 0.03) × 10−7 for every electron deposited in a neighboring pixel (sensor chip assembly [SCA] 20829, statistical error, not IPC-deconvolved). We compare IPC maps from flat field autocorrelation measurements to those obtained from the single pixel reset method and find a median difference of 0.113% for SCA 20829. After further diagnosis of this difference, we ascribe it largely to an additional source of cross-talk, the vertical trailing pixel effect, and recommend further work to develop a model for this effect. These results represent a significant step toward calibration of the non-ideal effects in WFIRST detectors.

Separating the intrinsic alignment signal and the lensing signal using self-calibration in photo-z surveys with KiDS450 and KV450 Data

ABSTRACT To reach the full potential for the next generation of weak lensing surveys, it is necessary to mitigate the contamination of intrinsic alignments (IAs) of galaxies in the observed cosmic shear signal. The self-calibration (SC) of IAs provides an independent method to measure the IA signal from the survey data and the photometric redshift information. It operates differently from the marginalization method based on the IA modelling. In this work, we present the first application of SC to the KiDS450 data and the KV450 data, to split directly the intrinsic shape–galaxy density (Ig) correlation signal and the gravitational shear–galaxy density (Gg) correlation signal, using the information from photometric redshift (photo-z). We achieved a clear separation of the two signals and performed several validation tests. Our measured signals are found to be in general agreement with the KiDS450 cosmic shear best-fitting cosmology, for both lensing and IA measurements. For KV450, we use partial (high-z) data, and our lensing measurements are also in good agreement with KV450 cosmic shear best fit, while our IA signal suggests a larger IA amplitude for the high-z sample. We discussed the impact of photo-z quality on IA detection and several other potential systematic biases. Finally, we discuss the potential application of the information extracted for both the lensing signal and the IA signal in future surveys.

Chronic Hemodynamic Overload of the Atria is an Important Factor for Shear Signaling Remodeling in Rat Hearts

Hemodynamic disturbances induced by hypertension, heart failure, and valve diseases lead atrial fibrillation. We have previously shown that shear stress induces proarrhythmic Ca2+ waves via connexin43 (Cx43) hemichannel opening, and that ATP release through the Cx43, in turn, activates P2Y1 receptors (P2Y1Rs) and P2X4 receptors (P2X4Rs) in rat atrial myocytes. To understand cellular mechanism for mechanically-induced atrial arrhythmia and role of shear signaling in this pathogenesis, we compared atrial shear signaling between sham-operated rats and the rats subjected to prolonged transverse aortic constriction (TAC). Atrial cell hypertrophy with higher fractional shortening and dilation of atrial chamber were observed at 5 weeks (wk) after TAC surgery. On 4-month (mon) after TAC surgery, more severe dilation in atrium with lower fractional shortening was detected. Whole-cell patch clamp studies revealed that shear-induced nonselective cation currents that are mediated by P2X4Rs (about 50%) and Cx43 (about 20%), were enhanced with hypertrophy, but they were no longer enhanced during atrial failure. Total Cx43 proteins and phosphorylated Cx43 at its ser-368 residue were gradually increased by TAC, which was consistent with larger shear-induced NMDG+ currents in TAC rat atrial myocytes. P2X4R expression increased in 5-wk-TAC atrial cells, but decreased in 4-mon-TAC atrial cells. On the other hand, P2Y1R-dependent longitudinal Ca2+ waves and P2Y1R expression were significantly increased by 4-mon-TAC. Our data suggest that Cx43-P2 receptor-mediated shear signaling is significantly altered by the progress of atrial dilation and volume overload, and that biphasic changes in P2X4R function and expression versus TAC duration may play a role in the progression from hypertrophy to failure in atrium subjected to aortic stenosis and increased afterload.

A gravitational lensing detection of filamentary structures connecting luminous red galaxies

We present a weak lensing detection of filamentary structures in the cosmic web, combining data from the Kilo-Degree Survey, the Red Cluster Sequence Lensing Survey, and the Canada-France-Hawaii Telescope Lensing Survey. The line connecting luminous red galaxies with a separation of 3 − 5 h−1 Mpc was chosen as a proxy for the location of filaments. We measured the average weak lensing shear around ∼11 000 candidate filaments selected in this way from the Sloan Digital Sky Survey. After nulling the shear induced by the dark matter haloes around each galaxy, we reported a 3.4σ detection of an anisotropic shear signal from the matter that connects them. Adopting a filament density profile, motivated from N-body simulations, the average density at the centre of these filamentary structures was found to be 15 ± 4 times the critical density.

Controlling and leveraging small-scale information in tomographic galaxy–galaxy lensing

ABSTRACT The tangential shear signal receives contributions from physical scales in the galaxy–matter correlation function well below the transverse scale at which it is measured. Since small scales are difficult to model, this non-locality has generally required stringent scale cuts or new statistics for cosmological analyses. Using the fact that uncertainty in these contributions corresponds to an uncertainty in the enclosed projected mass around the lens, we provide an analytic marginalization scheme to account for this. Our approach enables the inclusion of measurements on smaller scales without requiring numerical sampling over extra free parameters. We extend the analytic marginalization formalism to retain cosmographic (shear-ratio) information from small-scale measurements that would otherwise be removed due to modelling uncertainties, again without requiring the addition of extra sampling parameters. We test the methodology using simulated likelihood analysis of a Dark Energy Survey Year 5-like galaxy–galaxy lensing and galaxy clustering datavector. We demonstrate that we can remove parameter biases due to the presence of an unmodelled one-halo contamination of the galaxy–galaxy lensing signal, and use the shear-ratio information on small scales to improve cosmological parameter constraints.

Effectiveness of acoustic emission parameters to monitor the crack formation in refractories – Case study on castables of different brittleness

Variability of in-service loads justifies the broad range of microstructures in ceramic refractories used as high temperature industrial insulation. Application of the non-destructive technique of Acoustic Emission (AE) potentially provides an insight into the microstructural response to thermo-mechanical loads and enables rational material development and application. Regarding the multitude of existing AE approaches, effectiveness of a number of AE damage parameters was studied. The AE parameters were obtained in cyclic three-point bending for refractory castables showing different brittleness at failure. No significant damping effects and good correlation with material brittleness was seen for the parameters of event counts, b-value, and AF/RA ratio. The loads introducing critical damage obtained from LOAD and CALM ratios of AE were in agreement with those indicated by AF/RA ratio and event counts during unloading. In the study, the parameter of AF/RA ratio differentiating between shear and tensile failure signals was seen as the most universal criterion.

Augmentation of Tissue Perfusion in Patients With Peripheral Artery Disease Using Microbubble Cavitation

ObjectivesThe authors investigated ideal acoustic conditions on a clinical scanner custom-programmed for ultrasound (US) cavitation-mediated flow augmentation in preclinical models. We then applied these conditions in a first-in-human study to test the hypothesis that contrast US can increase limb perfusion in normal subjects and patients with peripheral artery disease (PAD). BackgroundUS-induced cavitation of microbubble contrast agents augments tissue perfusion by convective shear and secondary purinergic signaling that mediates release of endogenous vasodilators. MethodsIn mice, unilateral exposure of the proximal hindlimb to therapeutic US (1.3 MHz, mechanical index 1.3) was performed for 10 min after intravenous injection of lipid microbubbles. US varied according to line density (17, 37, 65 lines) and pulse duration. Microvascular perfusion was evaluated by US perfusion imaging, and in vivo adenosine triphosphate (ATP) release was assessed using in vivo optical imaging. Optimal parameters were then used in healthy volunteers and patients with PAD where calf US alone or in combination with intravenous microbubble contrast infusion was performed for 10 min. ResultsIn mice, flow was augmented in the US-exposed limb for all acoustic conditions. Only at the lowest line density was there a stepwise increase in perfusion for longer (40-cycle) versus shorter (5-cycle) pulse duration. For higher line densities, blood flow consistently increased by 3-fold to 4-fold in the US-exposed limb irrespective of pulse duration. High line density and long pulse duration resulted in the greatest release of ATP in the cavitation zone. Application of these optimized conditions in humans together with intravenous contrast increased calf muscle blood flow by >2-fold in both healthy subjects and patients with PAD, whereas US alone had no effect. ConclusionsUS of microbubbles when using optimized acoustic environments can increase perfusion in limb skeletal muscle, raising the possibility of a therapy for patients with PAD. (Augmentation of Limb Perfusion With Contrast Ultrasound; NCT03195556)

Radio–optical galaxy shape and shear correlations in the COSMOS field using 3 GHz VLA observations

Abstract We present a weak-lensing analysis of the 3 GHz Very Large Array radio survey of the COSMOS field, which we correlate with overlapping Hubble Space Telescope-Advanced Camera for Survey optical observations using both intrinsic galaxy shape and cosmic shear correlation statistics. After cross-matching sources between the two catalogues, we measure the correlations of galaxy position angles and find a Pearson correlation coefficient of 0.14 ± 0.03. This is a marked improvement from previous studies which found very weak, or non-existent correlations, and gives insight into the emission processes of radio and optical galaxies. We also extract power spectra of averaged galaxy ellipticities (the primary observable for cosmic shear) from the two catalogues, and produce optical–optical, radio–optical, and radio–radio spectra. The optical–optical autopower spectrum was measured to a detection significance of 9.80σ and is consistent with previous observations of the same field. For radio spectra (which we do not calibrate, given the unknown nature of their systematics), although we do not detect significant radio–optical (1.50σ) or radio–radio (1.45σ) E-mode power spectra, we do find the E-mode spectra to be more consistent with the shear signal expected from previous studies than with a null signal, and vice versa for B-mode and EB cross-correlation spectra. Our results give promise that future radio weak-lensing surveys with larger source number densities over larger areas will have the capability to measure significant weak-lensing signals.

The case for two-dimensional galaxy–galaxy lensing

We revisit the performance and biases of the two-dimensional approach to galaxy–galaxy lensing. This method exploits the information for the actual positions and ellipticities of source galaxies, rather than using only the ensemble properties of statistically equivalent samples. We compare the performance of this method with the traditionally used one-dimensional tangential shear signal on a set of mock data that resemble the current state-of-the-art weak lensing surveys. We find that under idealised circumstances the confidence regions of joint constraints for the amplitude and scale parameters of the NFW model in the two-dimensional analysis can be more than three times tighter than the one-dimensional results. Moreover, this improvement depends on the lens number density and it is larger for higher densities. We compare the method against the results from the hydrodynamical EAGLE simulation in order to test for possible biases that might arise due to lens galaxies being missed, and find that the method is able to return unbiased estimates of halo masses when compared to the true properties of the EAGLE galaxies. Because of its advantage in high galaxy density areas, the method is especially suitable for studying the properties of satellite galaxies in clusters of galaxies.

Luminous red galaxies in the Kilo-Degree Survey: selection with broad-band photometry and weak lensing measurements

We use the overlap between multiband photometry of the Kilo-Degree Survey (KiDS) and spectroscopic data based on the Sloan Digital Sky Survey (SDSS) and Galaxy And Mass Assembly (GAMA) to infer the colour-magnitude relation of red-sequence galaxies. We then use this inferred relation to select luminous red galaxies (LRGs) in the redshift range of $0.1<z<0.7$ over the entire KiDS Data Release 3 footprint. We construct two samples of galaxies with different constant comoving densities and different luminosity thresholds. The selected red galaxies have photometric redshifts with typical photo-z errors of $\sigma_z \sim 0.014 (1+z)$ that are nearly uniform with respect to observational systematics. This makes them an ideal set of galaxies for lensing and clustering studies. As an example, we use the KiDS-450 cosmic shear catalogue to measure the mean tangential shear signal around the selected LRGs. We detect a significant weak lensing signal for lenses out to $z \sim 0.7$.

Different Context for Shear Signaling in Left Versus Right Atrial Myocytes: Differential Roles of P2Y1- and P2X4-Purinoceptors

Different Context for Shear Signaling in Left Versus Right Atrial Myocytes: Differential Roles of P2Y1- and P2X4-Purinoceptors

Weak-lensing analysis of SPT-selected galaxy clusters using Dark Energy Survey Science Verification data

We present weak lensing (WL) mass constraints for a sample of massive galaxy clusters detected by the South Pole Telescope (SPT) via the Sunyaev-Zeldovich effect (SZE). We use $griz$ imaging data obtained from the Science Verification (SV) phase of the Dark Energy Survey (DES) to fit the WL shear signal of 33 clusters in the redshift range $0.25 \le z \le 0.8$ with NFW profiles and to constrain a four-parameter SPT mass-observable relation. To account for biases in WL masses, we introduce a WL mass to true mass scaling relation described by a mean bias and an intrinsic, log-normal scatter. We allow for correlated scatter within the WL and SZE mass-observable relations and use simulations to constrain priors on nuisance parameters related to bias and scatter from WL. We constrain the normalization of the $\zeta-M_{500}$ relation, $A_\mathrm{SZ}=12.0_{-6.7}^{+2.6}$ when using a prior on the mass slope $B_\mathrm{SZ}$ from the latest SPT cluster cosmology analysis. Without this prior, we recover $A_\mathrm{SZ}=10.8_{-5.2}^{+2.3}$ and $B_\mathrm{SZ}=1.30_{-0.44}^{+0.22}$. Results in both cases imply lower cluster masses than measured in previous work with and without WL, although the uncertainties are large. The WL derived value of $B_\mathrm{SZ}$ is $\approx 20\%$ lower than the value preferred by the most recent SPT cluster cosmology analysis. The method demonstrated in this work is designed to constrain cluster masses and cosmological parameters simultaneously and will form the basis for subsequent studies that employ the full SPT cluster sample together with the DES data.

Deep lensing with a twist: E and B modes in a field with multiple lenses

We explore the weak lensing E- and B-mode shear signals of a field of galaxy clusters using both large scale structure N-body simulations and multi-color Suprime-cam & Hubble Space Telescope observations. Using the ray-traced and observed shears along with photometric redshift catalogs, we generate mass maps of the foreground overdensities by optimally filtering the tangential shear that they induce on background galaxies. We then develop and test a method to approximate the foreground structure as a superposition of NFW-like halos by locating these overdensities and determining their mass and redshift, thereby modeling the background correlated shear field as a sum of lensings induced by the foreground clusters. We demonstrate that the B-mode maps and shear correlation functions, which are generated by similarly filtering the cross shear in this method, are in agreement with observations and are related to the estimated cluster masses and locations as well as the distribution of background sources. Using the foreground mass model, we identify several sources of weak lensing B-modes including leakage and edge effects, source clustering, and multiple lensing which can be observed in deep cosmic shear surveys.

Fourier Power Function Shapelets (FPFS) shear estimator: performance on image simulations

We reinterpret the shear estimator developed by Zhang & Komatsu (2011) within the framework of Shapelets and propose the Fourier Power Function Shapelets (FPFS) shear estimator. Four shapelet modes are calculated from the power function of every galaxy's Fourier transform after deconvolving the Point Spread Function (PSF) in Fourier space. We propose a novel normalization scheme to construct dimensionless ellipticity and its corresponding shear responsivity using these shapelet modes. Shear is measured in a conventional way by averaging the ellipticities and responsivities over a large ensemble of galaxies. With the introduction and tuning of a weighting parameter, noise bias is reduced below one percent of the shear signal. We also provide an iterative method to reduce selection bias. The FPFS estimator is developed without any assumption on galaxy morphology, nor any approximation for PSF correction. Moreover, our method does not rely on heavy image manipulations nor complicated statistical procedures. We test the FPFS shear estimator using several HSC-like image simulations and the main results are listed as follows. (i) For simulations which only contain isolated galaxies, the amplitude of multiplicative bias is below 1 % . (ii) For more realistic simulations which also contain blended galaxies, the blended galaxies are deblended by the first generation HSC deblender before shear measurement. Multiplicative bias of (-5.71 +- 0.31) % is found. The blending bias is calibrated by image simulations. Finally, we test the consistency and stability of this calibration.

Cosmological simulations for combined-probe analyses: covariance and neighbour-exclusion bias

We present a public suite of weak lensing mock data, extending the Scinet Light Cone Simulations (SLICS) to simulate cross-correlation analyses with different cosmological probes. These mocks include KiDS-450- and LSST-like lensing data, cosmic microwave background lensing maps and simulated spectroscopic surveys that emulate the GAMA, BOSS and 2dFLenS galaxy surveys. With 844 independent realisations, our mocks are optimised for combined-probe covariance estimation, which we illustrate for the case of a joint measurement involving cosmic shear, galaxy-galaxy lensing and galaxy clustering from KiDS-450 and BOSS data. With their high spatial resolution, the SLICS are also optimal for predicting the signal for novel lensing estimators, for the validation of analysis pipelines, and for testing a range of systematic effects such as the impact of neighbour-exclusion bias on the measured tomographic cosmic shear signal. For surveys like KiDS and DES, where the rejection of neighbouring galaxies occurs within ~2 arcseconds, we show that the measured cosmic shear signal will be biased low, but by less than a percent on the angular scales that are typically used in cosmic shear analyses. The amplitude of the neighbour-exclusion bias doubles in deeper, LSST-like data. The simulation products described in this paper are made available at http://slics.roe.ac.uk/.