arXiv subjects

Toshiki Kurita

Publications and source records attributed to Toshiki Kurita.

At least 19 recordsLinked to original sources

arXiv2026

The Environmental Dependence of Halo Intrinsic Alignments: Stronger Signals in Underdense Regions

The intrinsic alignment (IA) of galaxies and the dark matter haloes that host them is one of the leading astrophysical systematics for weak-lensing cosmology, yet how the IA signal depends on the large-scale environment in which haloes reside is not yet fully characterised. We use the high-resolution $N$-body simulations of the Dark Quest suite to measure the environmental dependence of the IA of dark matter haloes over the redshift range $z=0.1$--$1.5$. We quantify each halo's environment through the overdensity $δ_8$, defined from the number of neighbouring haloes within $8\, h^{-1}Mpc$, and we isolate the environmental effect from its degeneracy with the halo-mass dependence by comparing the most overdense and most underdense haloes constructed to share the same halo-mass distribution. We find that haloes in underdense environments exhibit systematically larger IA amplitudes $A_{\rm IA}$ than haloes of the same mass in overdense environments, by a factor of $\sim1.5$--$1.8$, and that this trend persists across the mass and redshift ranges probed, strengthening towards low redshift. Using an orientation-only (unit-ellipticity) estimator, we further show that this environmental contrast is driven by a combination of two effects: haloes in underdense regions are both intrinsically less spherical and more strongly aligned with the large-scale tidal field than their overdense counterparts of the same mass. These results indicate that the large-scale environment is a non-negligible variable in modelling halo and galaxy alignments, and may be a particularly important factor for beyond-two-point weak-lensing analyses.

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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.

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arXiv2026

Parity Violation in Galaxy Shapes: Primordial Non-Gaussianity

We present a comprehensive study of galaxy intrinsic alignment (IA) as a probe of parity-violating primordial non-Gaussianity (PNG). Within the effective field theory (EFT) framework, we show that the parity-odd IA power spectrum is sensitive to the collapsed limit of the parity-odd primordial trispectrum. For a $U(1)$-gauge inflationary model, the IA power spectrum is proportional to the power spectrum of the curvature perturbation, $P_ζ(k) \propto k^{-3}$. However, the proportionality constants contain not only the PNG amplitude but also undetermined EFT bias parameters. We use $N$-body simulations to determine the bias parameters for dark matter halos. Using these bias parameters, we forecast IA's constraining power, assuming data from the Dark Energy Spectroscopic Instrument (DESI) and the Rubin Observatory Legacy Survey of Space and Time (LSST). We find that the IA power spectrum can improve the current limits on the amplitude of parity-violating PNG derived from galaxy four-point correlation and CMB trispectrum analyses. Moreover, galaxy shapes are complementary to these probes as they are sensitive to different scales and trispectrum configurations. Beyond galaxy shapes, we develop a new method to generate initial conditions for simulations and forward models from the parity-odd trispectrum with an enhanced collapsed limit.

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arXiv2025

The Bispectrum of Intrinsic Alignments: II. Precision Comparison Against Dark Matter Simulations

We measure three-dimensional bispectra of halo intrinsic alignments (IA) and dark matter overdensities in real space from N-body simulations for halos of mass $10^{12}-10^{12.5} M_\odot /h$. We show that their multipoles with respect to the line of sight can be accurately described by a tree-level perturbation theory model on large scales ($k\lesssim 0.11\,h$/Mpc) at $z=0$. For these scales and in a simulation volume of 1 (Gpc/$h)^3$, we detect the bispectrum monopole $B_{δδE}^{00}$ at SNR $\sim 30$ and the two quadrupoles $B_{δδE}^{11}$ and $B_{δδE}^{20}$ at SNR $\sim 25$ and SNR $\sim 15$, respectively. We also report similar SNR for the lowest order multipoles of $B_{δEE}$ and $B_{EEE}$, although these are largely driven by stochastic contributions. We show that the first and second order EFT parameters are consistent with those obtained from fitting the IA power spectrum analysis at next-to-leading order, without requiring any priors to break degeneracies for the quadratic bias parameters. Moreover, the inclusion of higher multipole moments of $B_{δδE}$ greatly reduces the errors on second order bias parameters, by factors of 5 or more. The IA bispectrum thus provides an effective means of determining higher order shape bias parameters, thereby characterizing the scale dependence of the IA signal. We also detect parity-odd bispectra such as $B_{δδB}$ and $B_{δEB}$ at $\sim 10 σ$ significance or more for $k<0.15\,h$/Mpc and they are consistent with the parity-even sector. Furthermore, we check that the Gaussian covariance approximation works reasonably well on the scales we consider here. These results lay the groundwork for using the bispectrum of IA in cosmological analyses.

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arXiv2025

Nonlinear Evolution of the Matter Trispectrum with Primordial Parity Violation

Parity-odd four-point correlation functions, or trispectra, of cosmic matter density fields provide a unique probe of fundamental symmetries in cosmology. Trispectra of primordial matter density fluctuations produced in the early universe are modified by the subsequent nonlinear structure formation. In this paper, we compute the nonlinear evolution of the parity-odd matter trispectrum to one-loop order, i.e., to third order in density fluctuations, within the framework of effective field theory of the large-scale structure of the universe. By analyzing the different terms in the perturbation series, we demonstrate the structure of infrared divergence cancellations, as required by the equivalence principle. We also derive the forms of the counterterms required to renormalize the ultraviolet divergences. Adopting a specific model for a primordial parity-odd trispectrum, we numerically compute the leading-order effects of nonlinear gravitational evolution and study its impact on baryonic acoustic oscillations within the signal. These calculations are essential for comparing the observed trispectra of nonlinear cosmic density fields with theoretical expectations.

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arXiv2025

The Bispectrum of Intrinsic Alignments: Theory Modelling and Forecasts for Stage IV Galaxy Surveys

We present a complete treatment of the bispectrum of intrinsic alignments, both in three spatial dimensions and in projection in the flat-sky approximation. Since intrinsic alignment is a spin-2 observable, the bispectrum of intrinsic alignments contains a parity-even and a parity-odd part, the latter being nonzero even in the absence of parity violation. Moreover, all possible combinations of scalar, E- and B-mode bispectra are nonzero in the absence of parity violation. In analogy to the galaxy bispectrum in redshift space, we construct a complete set of multipoles for anisotropic bispectra of projected spin-2 fields. We then construct separable bispectrum estimators, both for parity-even and parity-odd bispectra, which can be computed by means of Fast Fourier Transforms (FFTs). We compare several different choices of angular weighting in terms of signal-to-noise ratios (SNR) for a Stage IV setup using luminous red galaxies (LRGs) from the Dark Energy Spectroscopic Instrument (DESI) with galaxy shapes measured by the Legacy Survey of Space and Time (LSST). Assuming an overlapping area of $\sim 4,000$ square degrees (yielding $\sim 1.3$ million LRGs) and including scales up to $k_\text{max} = 0.14\,h$/Mpc, we find that the position-position-E-mode bispectrum $B_{DDE}$ (which is parity-even) can be strongly detected at SNR $\sim 30$, while detecting parity-odd bispectra (such as $B_{DDB}$, SNR $\sim 5$) or bispectra with more than one shape field (such as $B_{DEE}$, SNR $\sim 5$) may also be possible.

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arXiv2025

Improving redshift-space power spectra of halo intrinsic alignments from perturbation theory

Intrinsic alignments (IAs) of galaxies/halos observed via galaxy imaging survey, combined with redshift information, offer a novel probe of cosmology as a tracer of the tidal force field of a large-scale structure. In this paper, we present a perturbation theory based model for the redshift-space power spectra of galaxy/halo IAs that can keep the impact of the Finger-of-God damping effect, known as a nonlinear systematics of redshift-space distortions, under control. Focusing particularly on galaxy/halo density and an IA cross power spectrum, we derive analytically the explicit expressions for the next-to-leading order corrections. Comparing the model predictions with $N$-body simulations, we show that these corrections indeed play an important role for an unbiased determination of the growth-rate parameter, and hence the model proposed here can be used for a precision test of gravity on cosmological scales.

astro-ph.CO↗

arXiv2025

Fully non-linear simulations of galaxy intrinsic alignments for weak lensing with the MillenniumTNG lightcone

We present a complete forward model of a realistic weak lensing galaxy catalogue based on the 740 Mpc hydrodynamical MillenniumTNG (MTNG) simulation. Starting with a complete particle and cell lightcone covering one octant of the sky with redshift range 0 < $z$ < 1.5, we apply a group and subhalo finder to generate the corresponding galaxy catalogue for a fiducial observer. For all galaxies, we compute both their intrinsic and lensing-induced shear. The intrinsic component is derived from the luminosity-weighted inertia tensor of stellar particles, while the extrinsic (gravitational) shear is obtained through full-sky ray-tracing on the same lightcone. This allows us to directly predict the impact of intrinsic alignment (IA) of galaxies on the shear correlation function and popular convergence statistics in a fully non-linear forward model. We find that IA modifies the convergence power spectrum at all angular scales by up to 20%, it significantly impacts the PDF, altering its tails by 10-20%, and distorts peak and minimum counts up to 30%, depending on redshift and scale. We also evaluate the impact of the IA signal on the shear correlation function finding that, along with a redshift dependence, the signal strongly increases for higher galaxy stellar mass cuts applied to the catalogue. Notably, with the highest stellar mass cut we apply, the intrinsic shear autocorrelation can become comparable to the gravitational shear component on small angular scales. Our results highlight the importance of accurately modeling IA for precision weak lensing cosmology with upcoming Stage IV surveys.

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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↗

arXiv2024

HYMALAIA: A Hybrid Lagrangian Model for Intrinsic Alignments

The intrinsic alignment of galaxies is an important ingredient for modelling weak-lensing measurements, and a potentially valuable cosmological and astrophysical signal. In this paper, we present HYMALAIA: a new model to predict the intrinsic alignments of biased tracers. HYMALAIA is based on a perturbative expansion of the statistics of the Lagrangian shapes of objects, which is then advected to Eulerian space using the fully non-linear displacement field obtained from $N$-body simulations. We demonstrate that HYMALAIA is capable of consistently describing monopole and quadrupole of halo shape-shape and matter-shape correlators, and that, without increasing the number of free parameters, it does so more accurately than other perturbatively inspired models such as the non-linear alignment (NLA) model and the tidal-alignment-tidal-torquing (TATT) model.

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arXiv2024

Nonlinear redshift space distortion in halo ellipticity correlations: Analytical model and N-body simulations

We present an analytic model of nonlinear correlators of galaxy/halo ellipticities in redshift space. The three-dimensional ellipticity field is not affected by the redshift-space distortion (RSD) at linear order, but by the nonlinear one, known as the Finger-of-God effect, caused by the coordinate transformation from real to redshift space. Adopting a simple Gaussian damping function to describe the nonlinear RSD effect and the nonlinear alignment model for the relation between the observed ellipticity and underlying tidal fields, we derive analytic formulas for the multipole moments of the power spectra of the ellipticity field in redshift space expanded in not only the associated Legendre basis, a natural basis for the projected galaxy shape field, but also the standard Legendre basis, conventionally used in literature. The multipoles of the corresponding correlation functions of the galaxy shape field are shown to be expressed by a simple Hankel transform, as is the case for those of the conventional galaxy density correlations. We measure these multipoles of the power spectra and correlation functions of the halo ellipticity field using large-volume N-body simulations. We then show that the measured alignment signals can be better predicted by our nonlinear model than the existing linear alignment model. The formulas derived here have already been used to place cosmological constraints using from the redshift-space correlation functions of the galaxy shape field measured from the Sloan Digital Sky Survey (Okumura and Taruya, 2023).

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↗

arXiv2024

The Intrinsic Alignment of Galaxy Clusters and Impact of Projection Effects

Galaxy clusters, being the most massive objects in the Universe, exhibit the strongest alignment with the large-scale structure. However, mis-identification of members due to projection effects from the large scale structure can occur. We studied the impact of projection effects on the measurement of the intrinsic alignment of galaxy clusters, using galaxy cluster mock catalogs. Our findings showed that projection effects result in a decrease of the large scale intrinsic alignment signal of the cluster and produce a bump at $r_p\sim 1h^{-1}/Mpc$, most likely due to interlopers and missed member galaxies. This decrease in signal explains the observed similar alignment strength between bright central galaxies and clusters in the SDSS redMaPPer cluster catalog. The projection effect and cluster intrinsic alignment signal are coupled, with clusters having lower fractions of missing members or having higher fraction of interlopers exhibiting higher alignment signals in their projected shapes. We aim to use these findings to determine the impact of projection effects on galaxy cluster cosmology in future studies.

astro-ph.CO↗

arXiv2023

Effective Field Theory of Intrinsic Alignments at One Loop Order: a Comparison to Dark Matter Simulations

We test the regime of validity of the effective field theory (EFT) of intrinsic alignments (IA) at the one-loop level by comparing with 3D halo shape statistics in N-body simulations. This model is based on the effective field theory of large-scale structure (EFT of LSS) and thus a theoretically well-motivated extension of the familiar non-linear alignment (NLA) model and the tidal-alignment-tidal-torquing (TATT) model. It contains a total of $8$ free bias parameters. Specifically, we measure the dark matter halo shape-shape multipoles $P_{EE}^{(0)}(k), P_{EE}^{(2)}(k), P_{BB}^{(0)}(k), P_{BB}^{(2)}(k)$ as well as the matter-shape multipoles $P_{δE}^{(0)}(k), P_{δE}^{(2)}(k)$ from the simulations and perform a joint fit to determine the largest wavenumber $k_{\text{max}}$ up to which the theory predictions from the EFT of IA are consistent with the measurements. We find that the EFT of IA is able to describe intrinsic alignments of dark matter halos up to $k_\text{max}=0.30\,h/\text{Mpc}$ at $z=0$. This demonstrates a clear improvement over other existing alignment models like NLA and TATT, which are only accurate up to $k_\text{max}=0.05\,h/\text{Mpc}$ . We examine the posterior distributions of the higher-order bias parameters, and show that their inclusion is necessary to describe intrinsic alignments in the quasi-linear regime. Further, the EFT of IA is able to accurately describe the auto-spectrum of intrinsic alignment B-modes, in contrast to the other alignment models considered.

astro-ph.CO↗

arXiv2023

Constraints on anisotropic primordial non-Gaussianity from intrinsic alignments of SDSS-III BOSS galaxies

We measure the three-dimensional cross-power spectrum of galaxy density and intrinsic alignment (IA) fields for the first time from the spectroscopic and imaging data of SDSS-III BOSS galaxies, for each of the four samples in the redshift range $0.2 < z < 0.75$. In the measurement we use the power spectrum estimator, developed in our previous work, to take into account the line-of-sight dependent projection of galaxy shapes onto the sky coordinate and the $E/B$-mode decomposition of the spin-2 shape field. Our method achieves a significant detection of the $E$-mode power spectrum with the total signal-to-noise ratio comparable with that of the quadrupole moment of the galaxy density power spectrum, while the measured $B$-mode power spectra are consistent with a null signal to within the statistical errors for all the galaxy samples. We also show that, compared to the previous results based on the two-dimensional projected correlation function, our method improves the precision of the linear shape bias parameter estimation by up to a factor of two thanks to the three-dimensional information. By performing a joint analysis of the galaxy density and IA power spectra in the linear regime, we constrain the isotropic and anisotropic local primordial non-Gaussianities (PNGs) parameters, $f_\mathrm{NL}^{s=0}$ and $f_\mathrm{NL}^{s=2}$, simultaneously, where the two types of PNGs induce characteristic scale-dependent biases at very large scales in the density and IA power spectra, respectively. We do not find any significant detection for both PNGs: the constraints $f^{s=0}_\mathrm{NL}=57^{+30}_{-29}$ and $f^{s=2}_\mathrm{NL} = -67_{-269}^{+285}$ ($68\%$ C.L.), respectively. Our method paves the way for using the IA power spectrum as a cosmological probe for current and future galaxy surveys.

astro-ph.CO↗

arXiv2022

Analysis method for 3D power spectrum of projected tensor field with fast estimator and window convolution modelling: an application to intrinsic alignments

Rank-2 tensor fields of large-scale structure, e.g. a tensor field inferred from shapes of galaxies, open up a window to directly access 2-scalar, 2-vector and 2-tensor modes, where the scalar fields can be measured independently from the standard density field that is traced by distribution of galaxies. Here we develop an estimator of the multipole moments of power spectra for the three-dimensional tensor field, taking into account the projection onto plane perpendicular to the line-of-sight direction. To do this, we find that a convenient representation of the power spectrum multipoles can be obtained by the use of the associated Legendre polynomials in the form which allows for the fast Fourier transform estimations under the local plane-parallel (LPP) approximation. The formulation also allows us to obtain the Hankel transforms to connect the two-point statistics in Fourier and configuration space, which are needed to derive theoretical templates of the power spectrum including convolution of a survey window. To validate our estimators, we use the simulation data of the projected tidal field assuming a survey window that mimics the BOSS-like survey footprint. We show that the LPP estimators fairly well recover the multipole moments that are inferred from the global plane-parallel approximation. We find that the survey window causes a more significant change in the multipole moments of projected tensor power spectrum at $k\lesssim 0.1\,h{\rm Mpc}^{-1}$ from the input power spectrum, than in the density power spectrum. Nevertheless, our method to compute the theory template including the survey window effects successfully reproduces the window-convolved multipole moments measured from the simulations. The analysis method presented here paves the way for a cosmological analysis using three-dimensional tensor-type tracers of large-scale structure for current and future surveys.

astro-ph.CO↗

arXiv2021

An Optimal Estimator of Intrinsic Alignments for Star-forming Galaxies in IllustrisTNG Simulation

Emission line galaxies (ELGs), more generally star-forming galaxies, are valuable tracers of large-scale structure and therefore main targets of upcoming wide-area spectroscopic galaxy surveys. We propose a fixed-aperture shape estimator of each ELG for extracting the intrinsic alignment (IA) signal, and assess the performance of the method using image simulations of ELGs generated from the IllustrisTNG simulation including observational effects such as the sky background noise. We show that our method enables a significant detection of the IA power spectrum with the linear-scale coefficient $A_{\rm IA}\simeq (13$--$15)\pm 3.0$ up to $z=2$, even from the small simulation volume $\sim0.009\,(h^{-1}{\rm Gpc})^3$, in contrast to the null detection with the standard method. Thus the ELG IA signal, measured with our method, opens up opportunities to exploit cosmology and galaxy physics in high-redshift universe.

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