arXiv subjects

Ryo Terasawa

Publications and source records attributed to Ryo Terasawa.

13 recordsLinked to original sources

arXiv2026

Modeling survey-window and integral-constraint effects on PNG in the galaxy power spectrum with light-cone mocks

We develop an analysis framework based on {\em light-cone} galaxy mock catalogs constructed from linear theory simulations in order to accurately model the impact of primordial non-Gaussianity (PNG) on galaxy power spectrum on large scales. These linear light-cone catalogs properly incorporate a variety of observational and cosmological effects, including the survey window function, the redshift evolution of matter and galaxy density fields, and redshift-space distortions (RSD). When estimating the multipole moments of the power spectrum from each light-cone mock, we employ the same estimator as used in actual analyses, thereby properly accounting for the effects of the discrete Fourier transform, the line-of-sight dependence of the fields, and wide-angle RSD effects. Using light-cone mock catalogs that mimic the BOSS survey, we demonstrate that long-wavelength modes comparable to or larger than the survey window scale, namely super-survey modes, have a significant impact on the integral constraint (IC) in power spectrum measurements. In particular, we show that the analytical treatment of the survey-window convolution and IC, which has been commonly used in previous studies, begins to lose accuracy on scales of $k\lesssim k_{\rm eq}$ (the matter-radiation equality scale), and becomes invalid in the presence of PNG. The method developed in this work enables unbiased searches for PNG using the galaxy power spectrum on long-wavelength scales probed by ongoing and future wide-area galaxy surveys.

astro-ph.CO↗

arXiv2026

Analytical method for computing the covariance matrix of cosmic shear two-point correlation function

Accurate estimation of the covariance matrix of cosmic shear statistics is essential for cosmological analyses using current and upcoming wide-area weak lensing surveys. In this work, we investigate analytical methods for computing the Gaussian covariance matrix of the cosmic shear two-point correlation function (2PCF), taking into account the effects of finite survey geometry. We compute the covariance of 2PCF based on the improved Narrow Kernel Approximation (iNKA), with a projection using the Legendre transformation. We also consider other analytical covariance estimators, the $f_{\mathrm{sky}}$ approximation and the weighted quartic-counts method. We evaluate the accuracy of those analytical methods using the convergence fields with the HSC Year 3 survey mask as a test case. We find that the covariance of the 2PCF obtained by using the iNKA does not reproduce the covariance measured directly from Gaussian simulations. Although the iNKA accurately models the diagonal structure of the harmonic-space covariance, residual inaccuracies in the off-diagonal components propagate through the Legendre transformation and significantly affect the real-space covariance. In contrast, the weighted quartic-counts method shows better agreement with the simulations. Our results demonstrate that accurate modeling of the off-diagonal structure of the harmonic-space covariance is crucial for obtaining reliable covariance estimates of real-space weak lensing statistics in the presence of survey window effects.

astro-ph.CO↗

arXiv2025

The contribution from small scales on two-point shear analysis: comparison between power spectrum and correlation function

A known problem in cosmic shear two-point statistics is the apparent inconsistency between analyses performed in harmonic space (power spectrum) and real space (angular correlation). This arises mainly from two factors: first, scale cuts in one space correspond to soft cuts in the other, as the relationship between the two spaces is mediated by Bessel functions. For the same reason, astrophysical effects that are compact in one space may not be in the other, which can lead to biased parameter estimates. In this paper, we argue that these two statistics are complementary: we expect a robust theory to provide consistent constraints regardless of the chosen scale cuts. We present the consequences of pushing our analysis to smaller scales in both spaces, accounting for different models of Intrinsic Alignment and Baryonic Feedback in HSC Y3 data: we find that the harmonic-space analysis is significantly less sensitive to the specific modeling of small-scale physics, with model-choice-driven biases in $S_8$ being 2-3 times smaller than in real space. We show that using a flexible, simulation-based emulator for baryonic feedback (BACCO) in combination with the TATT model for intrinsic alignments provides the most consistent cosmological constraints between the two spaces when pushing to the smallest scales. In contrast, the standard HMCode-2016 model results in a $\sim 1.1\sigma$ tension between the two statistics. While harmonic space appears more robust for cosmological inference given current model uncertainties, real-space analyses offer a clearer separation of baryonic effects and will play a crucial role in distinguishing between baryonic feedback models in upcoming surveys.

astro-ph.CO↗

arXiv2025

Impact of Simulation Box Size for Weak Lensing: Replication and Super-Sample Effects

We quantify the bias caused by small simulation box size on weak lensing observables and covariances, considering both replication and super-sample effects for a range of higher-order statistics. Using two simulation suites -- one comprising large boxes ($3750\,h^{-1}{\rm Mpc}$) and another constructed by tiling small boxes ($625\,h^{-1}{\rm Mpc}$) -- we generate full-sky convergence maps and extract $10^\circ \times 10^\circ$ patches via a Fibonacci grid. We consider biases in the mean and covariance of the angular power spectrum, bispectrum (up to $\ell=3000$), PDF, peak/minima counts, and Minkowski functionals. By first identifying lines of sight that are impacted by replications, we find that replication causes a O$(10\%)$ bias in the PDF and Minkowski functionals, and a O$(1\%)$ bias in other summary statistics. Replication also causes a O$(10\%)$ bias in the covariances, increasing with source redshift and $\ell$, reaching $\sim25\%$ for $z_s=2.5$. We additionally show that replication leads to heavy biases (up to O$(100\%)$ at high redshift) when performing gnomonic projection on a patch that is centered along a direction of replication. We then identify the lines of sight that are minimally affected by replication, and use the corresponding patches to isolate and study super-sample effects, finding that, while the mean values agree to within $1\%$, the variances differ by O$(10\%)$ for $z_s\leq2.5$. We show that these effects remain in the presence of noise and smoothing scales typical of the DES, KiDS, HSC, LSST, Euclid, and Roman surveys. We also discuss how these effects scale as a function of box size. Our results highlight the importance of large simulation volumes for accurate lensing statistics and covariance estimation.

astro-ph.CO↗

arXiv2025

The impact of the redshift-dependent selection effect of halos on the redshift-space power spectrum

In a wide-area spectroscopic survey of galaxies, it is nearly impossible to obtain a homogeneous sample of galaxies with respect to galaxy properties such as stellar mass and host halo mass across a range of redshifts. Despite the selection effect, theoretical templates in most analyses assume single tracers when compared with the measured clustering quantities. We demonstrate analytically that the selection effect inevitably introduces a bias in the redshift-space power spectrum on scales from linear to nonlinear scales. To quantitatively assess the impact of the selection effect, we construct mock galaxy catalogs from halos in N-body simulations by selecting halos above redshift-dependent mass thresholds such that the resulting redshift distribution of the halos, $n(z)$, matches that of SDSS-like galaxies. We find that the selection effect causes fractional changes of up to only 1% and 2% in the monopole and quadrupole moments of the redshift-space power spectrum at $k\lesssim 0.3~h{\rm{Mpc}}^{-1}$, respectively, compared to the moments for the single mass-threshold (therefore single tracer) sample, for $n_{\rm g}(z)$ of the SDSS-like galaxy samples. We also argue that the selection effect is unlikely to cause a significant bias in the estimation of cosmological parameters using the Fisher matrix method, provided that the redshift-dependent selection effect is modest.

astro-ph.CO↗

arXiv2025

Late-time suppression of structure growth as a solution for the $S_8$ tension

The $S_8$ value inferred from the Subaru Hyper Suprime-Cam (HSC) Year 3 cosmic shear data, under the assumption of the flat $Λ$CDM model, is 2-3$σ$ lower than that inferred from observations of the early-time universe, such as cosmic microwave background (CMB) anisotropy data. Resolving the $S_8$ tension requires a scenario in which structure formation on small scales is suppressed in the late universe. As potential solutions, we consider extended models both within and beyond the $Λ$CDM model -- models that incorporate parameterized baryonic feedback effects, the effect of varying neutrino mass, and modified structure growth, each of which can lead to a suppression of structure growth at lower redshifts, with its own distinct scale- and redshift-dependencies. In particular, we consider phenomenological modified gravity models in which the suppression of structure growth is triggered at lower redshifts, as dark energy ($Λ$) begins to dominate the background expansion. We show that the modified growth factor models -- especially those featuring more rapid growth suppression at lower redshifts -- provide an improved fit to the combined datasets of the HSC-Y3 cosmic shear correlation functions, the Planck CMB, and the ACT DR6 CMB lensing, compared to the fiducial $Λ$CDM model and the models including the baryonic effects or the massive neutrino effect within the the $Λ$CDM framework.

astro-ph.CO↗

arXiv2025

Testing small-scale modifications in the primordial power spectrum with Subaru HSC cosmic shear, primary CMB and CMB lensing

Different cosmological probes, such as primary cosmic microwave background (CMB) anisotropies, CMB lensing, and cosmic shear, are sensitive to the primordial power spectrum (PPS) over different ranges of wavenumbers. In this paper, we combine the cosmic shear two-point correlation functions measured from the Subaru Hyper Suprime-Cam (HSC) Year 3 data with the Planck CMB data, and the ACT DR6 CMB lensing data to test modified shapes of the PPS at small scales, while fixing the background cosmology to the flat $Λ$CDM model. We consider various types of modifications to the PPS shape: the model with a running spectral index, the tanh-shaped model, the Starobinsky-type modification due to a sharp change in the inflaton potential, the broken power-law model, and the multiple broken power-law model. Although the HSC cosmic shear data is sensitive to the PPS at small scales, we find that the combined data remains consistent with the standard power-law PPS, i.e., the single power-law model, for the flat $Λ$CDM background. In other words, we conclude that the $S_8$ tension cannot be easily resolved by modifying the PPS within the $Λ$CDM background.

astro-ph.CO↗

arXiv2025

On the equivalence between galaxy angular correlation function and power spectrum in constraining primordial non-Gaussianity

We investigate the angular power spectrum ($C_\ell)$ and angular correlation function ($w(θ)$) of galaxy number density field in the presence of the local-type primordial non-Gaussianity (PNG), explicitly accounting for the integral constraint in an all-sky survey. We show that the PNG signature in $C_{\ell}$ is confined to low multipoles in the linear regime, whereas its signature in $w(θ)$ extends across a wide range of angular scales, including those below the nonlinear scale. Therefore, the equivalence between $C_\ell$ and $w(θ)$ can be violated when scale cuts of multipoles or angular scales -- for example, to mitigate systematic effects -- are applied in the analysis. Assuming samples of photometric galaxies divided into multiple redshift bins in the range $0<z<7$, we forecast the precision of constraining the PNG parameter ($f_{\rm NL}$) from the hypothetical measurements of $C_\ell$ or $w(θ)$ assuming different scale cuts in the multipoles or angular scales, respectively. Our results imply that the PNG information can be extracted from $w(θ)$ on relatively small angular scales such as $\lesssim 10$ degree for a high-redshift galaxy sample or from $w(θ)$ measured in a survey with partial area coverage.

astro-ph.CO↗

arXiv2024

Exploring the baryonic effect signature in the Hyper Suprime-Cam Year 3 cosmic shear two-point correlations on small scales: the $S_8$ tension remains present

The baryonic feedback effect is considered as a possible solution to the so-called $S_8$ tension indicated in cosmic shear cosmology. The baryonic effect is more significant on smaller scales, and affects the cosmic shear two-point correlation functions (2PCFs) with different scale- and redshift-dependencies from those of the cosmological parameters. In this paper, we use the Hyper Suprime-Cam Year 3 (HSC-Y3) data to measure the cosmic shear 2PCFs ($ξ_{\pm}$) down to 0.28 arcminutes, taking full advantage of the high number density of source galaxies in the deep HSC data, to explore a possible signature of the baryonic effect. While the published HSC analysis used the cosmic shear 2PCFs on angular scales, which are sensitive to the matter power spectrum at $k\lesssim 1~h{\rm Mpc}^{-1}$, the smaller scale HSC cosmic shear signal allows us to probe the signature of matter power spectrum up to $k\simeq 20~h{\rm Mpc}^{-1}$. Using the accurate emulator of the nonlinear matter power spectrum, DarkEmulator2, we show that the dark matter-only model can provide an acceptable fit to the HSC-Y3 2PCFs down to the smallest scales. In other words, we do not find any clear signature of the baryonic effects or do not find a systematic shift in the $S_8$ value with the inclusion of the smaller-scale information as would be expected if the baryonic effect is significant. Alternatively, we use a flexible 6-parameter model of the baryonic effects, which can lead to both enhancement and suppression in the matter power spectrum compared to the dark matter-only model, to perform the parameter inference of the HSC-Y3 2PCFs. We find that the small-scale HSC data allow only a fractional suppression of up to 5 percent in the matter power spectrum at $k\sim 1~h{\rm Mpc}^{-1}$, which is not sufficient to reconcile the $S_8$ tension.

astro-ph.CO↗

arXiv2023

Hyper Suprime-Cam Year 3 Results: Cosmology from Cosmic Shear Two-point Correlation Functions

We perform a blinded cosmology analysis with cosmic shear two-point correlation functions (2PCFs) measured from more than 25 million galaxies in the Hyper Suprime-Cam three-year shear catalog in four tomographic redshift bins ranging from 0.3 to 1.5. After conservative masking and galaxy selection, the survey covers 416 deg$^2$ of the northern sky with an effective galaxy number density of 15 arcmin$^{-2}$ over the four redshift bins. The 2PCFs adopted for cosmology analysis are measured in the angular range: $7.1 < θ/{\rm arcmin} < 56.6$ for $ξ_+$ and $31.2 <θ/{\rm arcmin} < 248$ for $ξ_-$, with a total signal-to-noise ratio of 26.6. We apply a conservative, wide, flat prior on the photometric redshift errors on the last two tomographic bins, and the relative magnitudes of the cosmic shear amplitude across four redshift bins allow us to calibrate the photometric redshift errors. With this flat prior on redshift errors, we find $Ω_{\rm m}=0.256_{-0.044}^{+0.056}$ and $S_8\equiv σ_8 \sqrt{Ω_{\rm m}/0.3}=0.769_{-0.034}^{+0.031}$ (both 68\% CI) for a flat $Λ$ cold dark matter cosmology. We find, after unblinding, that our constraint on $S_8$ is consistent with the Fourier space cosmic shear and the 3$\times$2pt analyses on the same HSC dataset. We carefully study the potential systematics from astrophysical and systematic model uncertainties in our fiducial analysis using synthetic data, and report no biases (including projection bias in the posterior space) greater than $0.5σ$ in the estimation of $S_8$. Our analysis hints that the mean redshifts of the two highest tomographic bins are higher than initially estimated. In addition, a number of consistency tests are conducted to assess the robustness of our analysis. Comparing our result with Planck-2018 cosmic microwave background observations, we find a ~$2σ$ tension for the $Λ$CDM model.

astro-ph.CO↗

arXiv2023

Flat to nonflat: Calculating nonlinear power spectra of biased tracers for nonflat $Λ$CDM model

The growth of large-scale structure, together with the geometrical information of cosmic expansion history and cosmological distances, can be used to obtain constraints on the spatial curvature of the universe that probes the early universe physics, whereas modeling the nonlinear growth in a nonflat universe is still challenging due to computational expense of simulations in a high-dimensional cosmological parameter space. In this paper, we develop an approximate method to compute the halo-matter and halo-auto power spectra for nonflat $Λ$CDM model, from quantities representing the nonlinear evolution of the corresponding flat $Λ$CDM model, based on the separate universe (SU) method. By utilizing the fact that the growth response to long-wavelength fluctuations (equivalently the curvature), $T_{δ_{\rm b}}(k)$, is approximated by the response to the Hubble parameter, $T_h(k)$, our method allows one to estimate the nonlinear power spectra in a nonflat universe efficiently from the power spectra of the flat universe. We use $N$-body simulations to show that the estimator can provide the halo-matter (halo-auto) power spectrum at $\sim 1\%$ ($\sim 2\%$ ) accuracy up to $k \simeq 3 (1) \, h {\rm Mpc}^{-1}$ even for a model with large curvature $Ω_K = \pm 0.1$. Using the estimator we can extend the prediction of the existing emulators such as Dark Emulator to nonflat models without degrading their accuracy. Since the response to long-wavelength fluctuations is also a key quantity for estimating the super sample covariance (SSC), we discuss that the approximate identity $T_{δ_{\rm b}}(k) \approx T_h(k)$ can be used to calculate the SSC terms analytically.

astro-ph.CO↗

arXiv2023

Super-sample covariance of the power spectrum, bispectrum, halos, voids, and their cross covariances

We study the effect of super-sample covariance (SSC) on the power spectrum and higher-order statistics: bispectrum, halo mass function, and void size function. We also investigate the effect of SSC on the cross covariance between the statistics. We consider both the matter and halo fields. Higher-order statistics of the large-scale structure contain additional cosmological information beyond the power spectrum and are a powerful tool to constrain cosmology. They are a promising probe for ongoing and upcoming high precision cosmological surveys such as DESI, PFS, Rubin Observatory LSST, Euclid, SPHEREx, SKA, and Roman Space Telescope. Cosmological simulations used in modeling and validating these statistics often have sizes that are much smaller than the observed Universe. Density fluctuations on scales larger than the simulation box, known as super-sample modes, are not captured by the simulations and in turn can lead to inaccuracies in the covariance matrix. We compare the covariance measured using simulation boxes containing super-sample modes to those without. We also compare with the Separate Universe approach. We find that while the power spectrum, bispectrum and halo mass function show significant scale- or mass-dependent SSC, the void size function shows relatively small SSC. We also find significant SSC contributions to the cross covariances between the different statistics, implying that future joint-analyses will need to carefully take into consideration the effect of SSC. To enable further study of SSC, our simulations have been made publicly available at https://github.com/HalfDomeSims/ssc.

astro-ph.CO↗

arXiv2022

Separate universe approach to evaluate nonlinear matter power spectrum for non-flat $Λ$CDM model

The spatial curvature ($Ω_K$) of the Universe is one of the most fundamental quantities that could give a link to the early universe physics. In this paper we develop an approximate method to compute the nonlinear matter power spectrum, $P(k)$, for "non-flat" $Λ$CDM models using the separate universe (SU) ansatz which states that the effect of the curvature on structure formation is equivalent to that of long-wavelength density fluctuation ($δ_{\rm b}$) in a local volume in the "flat" $Λ$CDM model, via the specific mapping between the background cosmological parameters and redshifts in the non-flat and flat models. By utilizing the fact that the normalized response of $P(k)$ to $δ_{\rm b}$ (equivalently $Ω_K$), which describes how the non-zero $Ω_K$ alters $P(k)$ as a function of $k$, is well approximated by the response to the Hubble parameter $h$ within the flat model, our method allows one to generalize the prediction of $P(k)$ for flat cosmologies via fitting formulae or emulators to that for non-flat cosmologies. We use $N$-body simulations for the non-flat $Λ$CDM models with $|Ω_K|\leq 0.1$ to show that our method can predict $P(k)$ for non-flat models up to $k \simeq 6\,h{\rm Mpc}^{-1}$ in the redshift range $z\simeq [0,1.5]$, to the fractional accuracy within $\sim 1$% that roughly corresponds to requirements for weak lensing cosmology with upcoming surveys. We find that the emulators, those built for flat cosmologies such as EuclidEmulator, can predict the non-flat $P(k)$ with least degradation.

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