arXiv subjects

Ryuichi Takahashi

Publications and source records attributed to Ryuichi Takahashi.

At least 55 records · Page 3Linked to original sources

arXiv2019

Mock galaxy shape catalogs in the Subaru Hyper Suprime-Cam Survey

We use the full-sky ray-tracing weak lensing simulations to generate 2268 mock catalogues for the Subaru Hyper Suprime-Cam (HSC) survey first-year shear catalogue. Our mock catalogues take into account various effects as in the real data: the survey footprints, inhomogeneous angular distribution of source galaxies, statistical uncertainties in photometric redshift (photo-$z$) estimate, variations in the lensing weight, and the statistical noise in galaxy shape measurements including both intrinsic shapes and the measurement errors. We then utilize our mock catalogues to evaluate statistical uncertainties expected in measurements of cosmic shear two-point correlations $ξ_{\pm}$ with tomographic redshift information for the HSC survey. We develop a quasi-analytical formula for the Gaussian sample variance properly taking into account the number of source pairs in the survey footprints. The standard Gaussian formula significantly overestimates or underestimates the mock results by $50\%$ level. We also show that different photo-$z$ catalogues or the six disconnected fields, rather than a consecutive geometry, cause variations in the covariance by $\sim 5\%$. The mock catalogues enable us to study the chi-square distribution for $ξ_{\pm}$. We find the wider distribution than that naively expected for the distribution with the degrees-of-freedom of data vector used. Finally, we propose a method to include non-zero multiplicative bias in mock shape catalogue and show the non-zero multiplicative bias can change the effective shape noise in cosmic shear analyses. Our results suggest an importance of estimating an accurate form of the likelihood function (and therefore the covariance) for robust cosmological parameter inference from the precise measurements.

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arXiv2019

Impact of nonlinear growth of the large-scale structure on CMB B-mode delensing

We study the impact of the nonlinear growth of the large-scale structure (LSS) on the removal of the gravitational lensing effect (delensing) in cosmic microwave background (CMB) $B$ modes. The importance of the nonlinear growth of the LSS in the gravitational lensing analysis of CMB has been recently recognized by several works, while its impact on delensing is not yet explored. The delensing using mass-tracers such as galaxies and cosmic infrared background (CIB) could be also affected by the nonlinear growth. We find that the nonlinear growth of the LSS leads to $\sim 0.3\%$ corrections to $B$-mode spectrum after delensing with a high-$z$ mass tracer ($z_m\sim 2$) at $\ell=1000$-$2000$. The off-diagonal correlation coefficients of the lensing $B$-mode template spectrum become significant for delensing with low-$z$ tracers ($z_m\lesssim 0.5$), but are negligible with high-$z$ tracers (such as CIB). On the other hand, the power spectrum covariance of the delensed $B$ mode is not significantly affected by the nonlinear growth of the LSS, and the delensing efficiency is not significantly changed even if we use low-$z$ tracers. The CMB $B$-mode internal delensing is also not significantly affected by the nonlinear growth.

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arXiv2018

CMB lensing bi-spectrum: assessing analytical predictions against full-sky lensing simulations

Cosmic microwave background (CMB) lensing is an integrated effect whose kernel is greater than half the peak value in the range $1<z<5$. Measuring this effect offers a powerful tool to probe the large-scale structure of the Universe at high redshifts. With the increasing precision of ongoing CMB surveys, other statistics than the lensing power spectrum, in particular the lensing bi-spectrum, will be measured at high statistical significance. This will provide ways to improve the constraints on cosmological models and lift degeneracies. Following on an earlier paper, we test analytical predictions of the CMB lensing bi-spectrum against full-sky lensing simulations, and discuss their validity and limitation in detail. The tree-level prediction of perturbation theory agrees with the simulation only up to $\ell\sim 200$, but the one-loop order allows capturing the simulation results up to $\ell\sim 600$. We also show that analytical predictions based on fitting formulas for the matter bi-spectrum agree reasonably well with simulation results, although the precision of the agreement depends on the configurations and scales considered. For instance, the agreement is at the $10\%$-level for the equilateral configuration at multipoles up to $\ell\sim2000$, but the difference in the squeezed limit raises to more than a factor of two at $\ell\sim2000$. This discrepancy appears to come from limitations in the fitting formula of the matter bi-spectrum. We also find that the analytical prediction for the post-Born correction to the bi-spectrum is in good agreement with the simulation. We conclude by discussing the bi-spectrum prediction in some theories of modified gravity.

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arXiv2018

Covariances for cosmic shear and galaxy-galaxy lensing in the response approach

In this study, we measure the response of matter and halo projected power spectra $P^{\rm 2D}_{\rm XY}(k)$ (X, Y are matter and/or halos), to a large-scale density contrast, $δ_{\rm b}$, using separate universe simulations. We show that the fractional response functions, i.e., $\mathrm{d}\ln P^{\rm 2D}_{\rm XY}(k)/\mathrm{d}δ_{\rm b}$, are identical to their respective three-dimensional power spectra within simulation measurement errors. Then, using various $N$-body simulation combinations (small-box simulations with periodic boundary conditions and sub-volumes of large-box simulations) to construct {mock observations of projected fields}, we study how super-survey modes, in both parallel and perpendicular directions to the projection direction, affect the covariance matrix of $P^{\rm 2D}_{\rm XY}(k)$, known as super-sample covariance (SSC). Our results indicate that the SSC term provides dominant contributions to the covariances of matter-matter and matter-halo spectra at small scales but does not provide significant contributions in the halo-halo spectrum. We observe that the large-scale density contrast in each redshift shell causes most of the SSC effect, and we did not observe a SSC signature arising from large-scale tidal field within the levels of measurement accuracy. We also develop a response approach to calibrate the SSC term for cosmic shear correlation function and galaxy--galaxy weak lensing, and validate the method by comparison with the light-cone ray-tracing simulations. Our method provides a reasonably accurate, albeit computationally inexpensive, way to calibrate the covariance matrix for clustering observables available from wide-area galaxy surveys.

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arXiv2018

Constraints on the mass-richness relation from the abundance and weak lensing of SDSS clusters

We constrain the scaling relation between optical richness ($λ$) and halo mass ($M$) for a sample of SDSS redMaPPer galaxy clusters within the context of the {\it Planck} cosmological model. We use a forward modeling approach where we model the probability distribution of optical richness for a given mass, $P(\ln λ| M)$. To model the abundance and the stacked lensing profiles, we use an emulator specifically built to interpolate the halo mass function and the stacked lensing profile for an arbitrary set of halo mass and redshift, which is calibrated based on a suite of high-resolution $N$-body simulations. We apply our method to 8,312 SDSS redMaPPer clusters with $20\le λ\le 100$ and $0.10\le z_λ\le0.33$, and show that the log-normal distribution model for $P(λ|M)$, with four free parameters, well reproduces the measured abundances and lensing profiles simultaneously. The constraints are characterized by the mean relation, $\left\langle \lnλ\right\rangle(M)=A+B\ln(M/M_{\rm pivot})$, with $A=3.207^{+0.044}_{-0.046}$ and $B=0.993^{+0.041}_{-0.055}$ (68\%~CL), where the pivot mass scale $M_{\rm pivot}=3\times 10^{14} h^{-1}M_\odot$, and the scatter $σ_{\mathrm{\lnλ}|M}=σ_0+q\ln(M/M_{\rm pivot})$ with $σ_0=0.456^{+0.047}_{-0.039}$ and $q=-0.169^{+0.035}_{-0.026}$. We find that a large scatter in halo masses is required at the lowest richness bins ($20\le λ\lesssim 30$) in order to reproduce the measurements. Without such a large scatter, the model prediction for the lensing profiles tends to overestimate the measured amplitudes. This might imply a possible contamination of intrinsically low-richness clusters due to the projection effects. Such a low-mass halo contribution is significantly reduced when applying our method to the sample of $30\le λ\le 100$.

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arXiv2017

The first-year shear catalog of the Subaru Hyper Suprime-Cam SSP Survey

We present and characterize the catalog of galaxy shape measurements that will be used for cosmological weak lensing measurements in the Wide layer of the first year of the Hyper Suprime-Cam (HSC) survey. The catalog covers an area of 136.9 deg$^2$ split into six fields, with a mean $i$-band seeing of $0.58$ arcsec and $5σ$ point-source depth of $i\sim 26$. Given conservative galaxy selection criteria for first year science, the depth and excellent image quality results in unweighted and weighted source number densities of 24.6 and 21.8 arcmin$^{-2}$, respectively. We define the requirements for cosmological weak lensing science with this catalog, then focus on characterizing potential systematics in the catalog using a series of internal null tests for problems with point-spread function (PSF) modeling, shear estimation, and other aspects of the image processing. We find that the PSF models narrowly meet requirements for weak lensing science with this catalog, with fractional PSF model size residuals of approximately $0.003$ (requirement: 0.004) and the PSF model shape correlation function $ρ_1<3\times 10^{-7}$ (requirement: $4\times 10^{-7}$) at 0.5$^\circ$ scales. A variety of galaxy shape-related null tests are statistically consistent with zero, but star-galaxy shape correlations reveal additive systematics on $>1^\circ$ scales that are sufficiently large as to require mitigation in cosmic shear measurements. Finally, we discuss the dominant systematics and the planned algorithmic changes to reduce them in future data reductions.

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arXiv2017

Full-sky Gravitational Lensing Simulation for Large-area Galaxy Surveys and Cosmic Microwave Background Experiments

We present 108 full-sky gravitational lensing simulation data sets generated by performing multiple-lens plane ray-tracing through high-resolution cosmological $N$-body simulations. The data sets include full-sky convergence and shear maps from redshifts $z=0.05$ to $5.3$ at intervals of $150 \, h^{-1}{\rm Mpc}$ comoving radial distance (corresponding to a redshift interval of $Δz \simeq 0.05$ at the nearby universe), enabling the construction of a mock shear catalog for an arbitrary source distribution up to $z=5.3$. The dark matter halos are identified from the same $N$-body simulations with enough mass resolution to resolve the host halos of the Sloan Digital Sky Survey (SDSS) CMASS and Luminous Red Galaxies (LRGs). Angular positions and redshifts of the halos are provided by a ray-tracing calculation, enabling the creation of a mock halo catalog to be used for galaxy-galaxy and cluster-galaxy lensing. The simulation also yields maps of gravitational lensing deflections for a source redshift at the last scattering surface, and we provide 108 realizations of lensed cosmic microwave background (CMB) maps in which the post-Born corrections caused by multiple light scattering are included. We present basic statistics of the simulation data, including the angular power spectra of cosmic shear, CMB temperature and polarization anisotropies, galaxy-galaxy lensing signals for halos, and their covariances. The angular power spectra of the cosmic shear and CMB anisotropies agree with theoretical predictions within $5\%$ up to $\ell = 3000$ (or at an angular scale $θ> 0.5$ arcsin). The simulation data sets are generated primarily for the ongoing Subaru Hyper Suprime-Cam survey but are freely available for download at http://cosmo.phys.hirosaki-u.ac.jp/takahasi/allsky_raytracing.

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arXiv2017

Robust covariance estimation of galaxy-galaxy weak lensing: validation and limitation of jackknife covariance

We develop a method to simulate galaxy-galaxy weak lensing by utilizing all-sky, light-cone simulations and their inherent halo catalogs. Using the mock catalog to study the error covariance matrix of galaxy-galaxy weak lensing, we compare the full covariance with the "jackknife" (JK) covariance, the method often used in the literature that estimates the covariance from the resamples of the data itself. We show that there exists the variation of JK covariance over realizations of mock lensing measurements, while the average JK covariance over mocks can give a reasonably accurate estimation of the true covariance up to separations comparable with the size of JK subregion. The scatter in JK covariances is found to be $\sim10\%$ after we subtract the lensing measurement around random points. However, the JK method tends to underestimate the covariance at the larger separations, more increasingly for a survey with a higher number density of source galaxies. We apply our method to the the Sloan Digital Sky Survey (SDSS) data, and show that the 48 mock SDSS catalogs nicely reproduce the signals and the JK covariance measured from the real data. We then argue that the use of the accurate covariance, compared to the JK covariance, allows us to use the lensing signals at large scales beyond a size of the JK subregion, which contains cleaner cosmological information in the linear regime.

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arXiv2016

Arrival time differences between gravitational waves and electromagnetic signals due to gravitational lensing

In this study, we demonstrate that general relativity predicts arrival time differences between gravitational wave (GW) and electromagnetic (EM) signals caused by the wave effects in gravitational lensing. The GW signals can arrive $earlier$ than the EM signals in some cases if the GW/EM signals have passed through a lens, even if both signals were emitted simultaneously by a source. GW wavelengths are much larger than EM wavelengths; therefore, the propagation of the GWs does not follow the laws of geometrical optics, including the Shapiro time delay, if the lens mass is less than approximately $10^5 {\rm M}_\odot (f/{\rm Hz})^{-1}$, where $f$ is the GW frequency. The arrival time difference can reach $\sim 0.1 \, {\rm s} \, (f/{\rm Hz})^{-1}$ if the signals have passed by a lens of mass $\sim 8000{\rm M}_\odot (f/{\rm Hz})^{-1}$ with the impact parameter smaller than the Einstein radius; therefore, it is more prominent for lower GW frequencies. For example, when a distant super massive black hole binary (SMBHB) in a galactic center is lensed by an intervening galaxy, the time lag becomes of the order of $10$ days. Future pulsar timing arrays including SKA (the Square Kilometre Array) and X-ray detectors may detect several time lags by measuring the orbital phase differences between the GW/EM signals in the SMBHBs. Gravitational lensing imprints a characteristic modulation on a chirp waveform; therefore, we can deduce whether a measured arrival time lag arises from intrinsic source properties or gravitational lensing. Determination of arrival time differences would be extremely useful in multimessenger observations and tests of general relativity.

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arXiv2016

The Subaru FMOS galaxy redshift survey (FastSound). IV. New constraint on gravity theory from redshift space distortions at $z\sim 1.4$

We measure the redshift-space correlation function from a spectroscopic sample of 2783 emission line galaxies from the FastSound survey. The survey, which uses the Subaru Telescope and covers the redshift ranges of $1.19<z<1.55$, is the first cosmological study at such high redshifts. We detect clear anisotropy due to redshift-space distortions (RSD) both in the correlation function as a function of separations parallel and perpendicular to the line of sight and its quadrupole moment. RSD has been extensively used to test general relativity on cosmological scales at $z<1$. Adopting a LCDM cosmology with the fixed expansion history and no velocity dispersion $σ_{\rm v}=0$, and using the RSD measurements on scales above 8Mpc/h, we obtain the first constraint on the growth rate at the redshift, $f(z)σ_8(z)=0.482\pm 0.116$ at $z\sim 1.4$ after marginalizing over the galaxy bias parameter $b(z)σ_8(z)$. This corresponds to $4.2σ$ detection of RSD. Our constraint is consistent with the prediction of general relativity $fσ_8\sim 0.392$ within the $1-σ$ confidence level. When we allow $σ_{\rm v}$ to vary and marginalize it over, the growth rate constraint becomes $fσ_8=0.494^{+0.126}_{-0.120}$. We also demonstrate that by combining with the low-z constraints on $fσ_8$, high-z galaxy surveys like the FastSound can be useful to distinguish modified gravity models without relying on CMB anisotropy experiments.

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arXiv2015

Detection of universality of dark matter profile from Subaru weak lensing measurements of 50 massive clusters

We develop a novel method of measuring the lensing distortion profiles of clusters with stacking the scaled amplitudes of background galaxy ellipticities as a function of the scaled centric radius according to the NFW prediction of each cluster, based on the assumption that the different clusters in a sample follow the universal NFW profile. First we demonstrate the feasibility of this method using both the analytical NFW model and simulated halos in high-resolution $N$-body simulations. We then apply, as a proof of concept, this method to the Subaru weak lensing data and the XMM/Chandra X-ray observables for a sample of 50 massive clusters in the redshift range $0.15\le z\le 0.3$, where their halo masses range over an order of magnitude. To estimate the NFW parameters of each cluster, we use the halo mass proxy relation of X-ray observables, based on either the hydrostatic equilibrium or the gas mass, and then infer the halo concentration from the model $c(M)$ relation. We evaluate a performance of the NFW scaling analysis by measuring the scatters of 50 cluster lensing profiles relative to the NFW predictions over a range of radii, $0.14\le R/[h^{-1}{\rm Mpc}]\le 2.8$. We found a 4 - 6$σ$ level evidence of the universal NFW profile in 50 clusters, for both the X-ray halo mass proxy relations, although the gas mass appears to be a better proxy of the underlying true mass. By comparing the measurements with the simulations of cluster lensing taking into account the statistical errors of intrinsic galaxy shapes in the Subaru data, we argue that additional halo mass errors or intrinsic scatters of $σ_{\ln M_{500c}}\sim 0.2$ - $0.3$ could reconcile a difference between the measurements and the simulations.

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arXiv2015

Constraints on small-scale cosmological fluctuations from SNe lensing dispersion

We provide predictions on small-scale cosmological density power spectrum from supernova lensing dispersion. Parameterizing the primordial power spectrum with running $α$ and running of running $β$ of the spectral index, we exclude large positive $α$ and $β$ parameters which induce too large lensing dispersions over current observational upper bound. We ran cosmological N-body simulations of collisionless dark matter particles to investigate non-linear evolution of the primordial power spectrum with positive running parameters. The initial small-scale enhancement of the power spectrum is largely erased when entering into the non-linear regime. For example, even if the linear power spectrum at $k>10h {\rm Mpc}^{-1}$ is enhanced by $1-2$ orders of magnitude, the enhancement much decreases to a factor of $2-3$ at late time ($z \leq 1.5$). Therefore, the lensing dispersion induced by the dark matter fluctuations weakly constrains the running parameters. When including baryon-cooling effects (which strongly enhance the small-scale clustering), the constraint is comparable or tighter than the PLANCK constraint, depending on the UV cut-off. Further investigations of the non-linear matter spectrum with baryonic processes is needed to reach a firm constraint.

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arXiv2015

Constraints on warm dark matter from weak lensing in anomalous quadruple lenses

We investigate the weak lensing effect by line-of-sight structures with a surface mass density of <~10^8 solar mass/arcsec^2 in QSO-galaxy quadruple lens systems. Using high-resolution N-body simulations in warm dark matter (WDM) models and observed four quadruple lenses that show anomalies in the flux ratios, we obtain constraints on the mass of thermal WDM, m_WDM>= 1.3keV(95%CL) assuming that the density of the primary lens is described by a singular isothermal ellipsoid (SIE). The obtained constraint is consistent with those from Lyman-$α$ forests and the number counts of high-redshift galaxies at z>4. Our results show that WDM with a free-streaming comoving wavenumber k_{fs} <= 27 h/Mpc is disfavored as the major component of cosmological density at redshifts 0.5 <~ z <~ 4 provided that the SIE models describe the gravitational potentials of the primary lenses correctly.

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arXiv2014

An optimal survey geometry of weak lensing survey: minimizing super-sample covariance

Upcoming wide-area weak lensing surveys are expensive both in time and cost and require an optimal survey design in order to attain maximum scientific returns from a fixed amount of available telescope time. The super-sample covariance (SSC), which arises from unobservable modes that are larger than the survey size, significantly degrades the statistical precision of weak lensing power spectrum measurement even for a wide-area survey. Using the 1000 mock realizations of the log-normal model, which approximates the weak lensing field for a $Λ$-dominated cold dark matter model, we study an optimal survey geometry to minimize the impact of SSC contamination. For a continuous survey geometry with a fixed survey area, a more elongated geometry such as a rectangular shape of 1:400 side-length ratio reduces the SSC effect and allows for a factor 2 improvement in the cumulative signal-to-noise ratio ($S/N$) of power spectrum measurement up to $\ell_{\rm max}\simeq $ a few $10^3$, compared to compact geometries such as squares or circles. When we allow the survey geometry to be disconnected but with a fixed total area, assuming $1\times 1$ sq. degrees patches as the fundamental building blocks of survey footprints, the best strategy is to locate the patches with $\sim 15$ degrees separation. This separation angle corresponds to the scale at which the two-point correlation function has a negative minimum. The best configuration allows for a factor 100 gain in the effective area coverage as well as a factor 2.5 improvement in the $S/N$ at high multipoles, yielding a much wider coverage of multipoles than in the compact geometry.

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arXiv2014

On the Systematic Errors of Cosmological-Scale Gravity Tests using Redshift Space Distortion: Non-linear Effects and the Halo Bias

Redshift space distortion (RSD) observed in galaxy redshift surveys is a powerful tool to test gravity theories on cosmological scales, but the systematic uncertainties must carefully be examined for future surveys with large statistics. Here we employ various analytic models of RSD and estimate the systematic errors on measurements of the structure growth-rate parameter, $fσ_8$, induced by non-linear effects and the halo bias with respect to the dark matter distribution, by using halo catalogues from 40 realisations of $3.4 \times 10^8$ comoving $h^{-3}$Mpc$^3$ cosmological N-body simulations. We consider hypothetical redshift surveys at redshifts z=0.5, 1.35 and 2, and different minimum halo mass thresholds in the range of $5.0 \times 10^{11}$ -- $2.0 \times 10^{13} h^{-1} M_\odot$. We find that the systematic error of $fσ_8$ is greatly reduced to ~5 per cent level, when a recently proposed analytical formula of RSD that takes into account the higher-order coupling between the density and velocity fields is adopted, with a scale-dependent parametric bias model. Dependence of the systematic error on the halo mass, the redshift, and the maximum wavenumber used in the analysis is discussed. We also find that the Wilson-Hilferty transformation is useful to improve the accuracy of likelihood analysis when only a small number of modes are available in power spectrum measurements.

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arXiv2014

Weak Lensing by Intergalactic Mini-Structures in Quadruple Lens Systems: Simulation and Detection

We investigate the weak lensing effects of line-of-sight structures on quadruple images in quasar-galaxy strong lens systems based on N-body and ray-tracing simulations that can resolve halos with a mass of 10^5 solar mass. The intervening halos and voids disturb the magnification ratios of lensed images as well as their relative positions due to lensing. The magnification ratios typically change by O(10%) when the shifts of relative angular positions of lensed images are constrained to <0.004 arcsec. The constrained amplitudes of projected density perturbations due to line-of-sight structures are O(10^8) solar mass per arcsec^2. These results are consistent with our new analytical estimate based on the two-point correlation of density fluctuations. The observed mid-infrared (MIR) flux ratios for 6 quasar-galaxy lens systems with quadruple images agree well with the numerically estimated values without taking into account of subhalos residing in the lensing galaxies. We find that the constrained mean amplitudes of projected density perturbations in the line-of-sight are negative, which suggests that the fluxes of lensed images are perturbed mainly by minivoids and minihalos in underdense regions. We derive a new fitting formula for estimating the probability distribution function of magnification perturbation. We also find that the mean amplitude of magnification perturbation roughly equals the standard deviation regardless of the model parameters.

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arXiv2013

Observational Upper Bound on the Cosmic Abundances of Negative-mass Compact Objects and Ellis Wormholes from the Sloan Digital Sky Survey Quasar Lens Search

The latest result in the Sloan Digital Sky Survey Quasar Lens Search (SQLS) has set the first cosmological constraints on negative-mass compact objects and Ellis wormholes. There are no multiple images lensed by the above two exotic objects for $\sim 50000$ distant quasars in the SQLS data. Therefore, an upper bound is put on the cosmic abundances of these lenses. The number density of negative mass compact objects is $n<10^{-8} (10^{-4}) h^3 {\rm Mpc}^{-3}$ at the mass scale $|M| > 10^{15} (10^{12}) M_\odot$, which corresponds to the cosmological density parameter $|Ω| < 10^{-4}$ at the galaxy-scale mass range $|M|=10^{12-15}M_\odot$. The number density of the Ellis wormhole is $n<10^{-4} h^3 {\rm Mpc}^{-3}$ for a range of the throat radius $a = 10^{1-4}$pc, which is much smaller than the Einstein ring radius.

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arXiv2013

Bias-Hardened CMB Lensing

We present new methods for lensing reconstruction from CMB temperature fluctuations which have smaller mean-field and reconstruction noise bias corrections than current lensing estimators, with minimal loss of signal-to-noise. These biases are usually corrected using Monte Carlo simulations, and to the extent that these simulations do not perfectly mimic the underlying sky there are uncertainties in the bias corrections. The bias-hardened estimators which we present can have reduced sensitivity to such uncertainties, and provide a desirable cross-check on standard results. To test our approach, we also show the results of lensing reconstruction from simulated temperature maps given on 100 deg^2, and confirm that our approach works well to reduce biases for a typical masked map in which 70 square masks each having 10 arcminute on a side exist, covering 2% of the simulated map, which is similar to the masks used in the current SPT lensing analysis.

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