arXiv subjects

Teppei Okumura

Publications and source records attributed to Teppei Okumura.

At least 19 recordsLinked to original sources

arXiv2026

Dipolar power asymmetry in wide-angle correlations of galaxy density, velocity and ellipticity

The large-scale structure of the universe has the potential to probe anomalies suggested by observations of the cosmic microwave background. In this work, we focus on a position-dependent dipolar modulation of the primordial power spectrum and develop a full-sky formalism for computing correlation functions of galaxy density, velocity and ellipticity. By comparing the correlation functions obtained with and without the plane-parallel approximation, we show that wide-angle corrections become non-negligible for opening angles $Θ\gtrsim 30^\circ$. Our results demonstrate that wide-angle corrections must be taken into account when testing the dipolar modulation with future large-scale structure surveys.

astro-ph.CO↗

arXiv2026

Probing dipolar power asymmetry with galaxy clustering and intrinsic alignments

We investigate the prospects for probing large-scale statistical anisotropy through galaxy clustering and intrinsic alignments (IA) in Stage IV galaxy surveys. Specifically, we consider a dipolar modulation in the primordial power spectrum and evaluate the Fisher information matrix using the two-point statistics of both the galaxy clustering and IA. Our analysis reveals that while IA alone provides limited improvement in constraining the anisotropy amplitude, the cross-spectrum between galaxy density and IA can contribute up to half the constraining power of galaxy clustering, especially for surveys with low galaxy bias and high number density of galaxies, such as Euclid. This demonstrates the potential of IA-clustering cross-correlations as a robust consistency check against systematics, and highlights the complementary roles of galaxy clustering and IA in constraining cosmic statistical anisotropy. We also show that marginalizing over galaxy bias and IA bias parameters has a negligible impact on the final constraint on the anisotropy amplitude.

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arXiv2026

Constraining Primordial Power Asymmetry from Galaxy Clustering and Peculiar Velocity Information

Primordial power asymmetry would probe departures from statistical isotropy, offering a clue to the physics of the primordial Universe. We investigate how such asymmetries can be tested with galaxy surveys and quantify how peculiar-velocity information can improve these tests. We develop a unified bipolar spherical harmonic (BipoSH) analysis of the auto- and cross-power spectra of galaxy density and line-of-sight peculiar velocity, and perform Fisher forecasts combining a Euclid-like spectroscopic galaxy survey with peculiar velocities reconstructed from Simons Observatory-like CMB maps through the kinetic Sunyaev-Zel'dovich effect. For dipolar asymmetry, we consider both scale-independent and scale-dependent modulations proportional to $k^{-0.5}$. Galaxy clustering provides most of the constraining power in both cases, while peculiar velocities add only modest information. For quadrupolar asymmetry, we account for the recently identified anisotropic galaxy-bias response and marginalize over its amplitude. We find that galaxy clustering alone suffers from a degeneracy between the primordial quadrupolar modulation and anisotropic galaxy bias. This degeneracy can be substantially broken by adding peculiar-velocity information: the density-velocity cross-spectrum provides complementary information to the galaxy auto-spectrum, while the velocity auto-spectrum constrains the primordial modulation independently of anisotropic galaxy bias. The velocity information becomes increasingly effective for more negative scale dependence, yielding constraints tighter than those from BOSS for scale dependences proportional to $k^{-1}$ and $k^{-2}$. Our results demonstrate that peculiar-velocity information provides a complementary avenue for testing primordial power asymmetry with large-scale structure, particularly for quadrupolar asymmetry in the presence of anisotropic galaxy bias.

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arXiv2026

Joint Geometric and Dynamical Constraints on Cosmology from Anisotropies in Galaxy Intrinsic-Alignment Correlations

We present the first joint cosmological analysis to extract both geometric and dynamical information from galaxy intrinsic alignments (IAs). Using BOSS spectroscopy cross-matched with galaxy shape measurements from the DESI Legacy Imaging Surveys, we measure anisotropic galaxy density--intrinsic ellipticity (GI) and intrinsic ellipticity (II) correlations over $0.43\leq z\leq0.7$ and decompose their spin-dependent angular structure into associated Legendre multipoles. The measured GI correlation exhibits the expected baryon acoustic oscillation (BAO) structure, while its anisotropy provides geometric information complementary to galaxy clustering. By jointly modeling redshift-space and Alcock-Paczynski distortions, we constrain the growth rate parameter $fσ_8$, the angular-diameter distance $D_A$, and the Hubble expansion rate $H$. Relative to galaxy clustering alone, adding IA reduces their fractional uncertainties by 32\%, 18\%, and 29\%, respectively. By mapping these constraints onto a flat $w_0$CDM model, IA also tightens the constraints on $w_0$, $Ω_m$, and $H_0$; however, the $w_0$ constraint is sensitive to the minimum scale included in the analysis. Our results establish anisotropic galaxy shapes as an additional source of geometric and dynamical information for spectroscopic cosmology.

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arXiv2026

Clustering of emission line galaxies with IllustrisTNG -- II. cosmology challenge with anisotropic correlation functions and ELG-halo connections

Emission line galaxies (ELGs) are the primary tracers of the large-scale structures of the Universe in ongoing Stage-IV cosmological spectroscopic surveys, which aim to measure the clustering statistics at higher redshifts $z \simeq 1.5 \text{--} 2$ with unprecedented precision. In this study, we construct realistic mock ELG samples with IllustrisTNG hydrodynamical simulations and stellar population synthesis framework. In order to validate the modelling of clustering, we measure the anisotropic correlation functions of mock ELGs and infer the linear growth rate, which is one of key cosmological parameters in galaxy clustering. As a control sample, we construct the mass-limited subhalo samples with the same number density as ELGs. The isotropic correlation functions in real space for both samples do not differ significantly. However, the quadrupole moment of the anisotropic correlation function, which is sensitive to the velocity of galaxies, is suppressed for ELGs, potentially due to the infalling motion of ELGs towards the centre of the hosting halos. The smaller amplitude leads to the underestimation of the linear growth rate and implies the velocity bias between ELGs and dark matter. When the analysis is limited to large scales $(\gtrsim 15 \, h^{-1} \, \mathrm{Mpc})$, the parameter bias vanishes. Next, we investigate the ELG-halo connection through the phase-space distribution of satellite ELGs within hosting halos and galactic conformity of star formation activity. The infalling motion is further confirmed by the phase-space distribution relative to the host halo, and this dynamics of ELGs challenges the assumption that the radial distribution of satellites follows that of dark matter.

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arXiv2026

Cosmological inference with halo clustering reconstructed from the redshift-space galaxy distribution

Accurate modeling of small-scale redshift-space clustering is crucial for full shape RSD analyses, where satellite galaxies contribute to 1-halo terms and Finger-of-God distortions. We investigate halo reconstruction based on the cylinder grouping (CG) method of Okumura et al. (2017), which selects an effective halo center tracer from the observed galaxy distribution, and how it impacts cosmological parameter inference. Using DESI-like luminous red galaxy mock catalogs from the AbacusSummit simulations at $z=1.1$, we perform effective field theory (EFT)-based full-shape modeling of the power spectrum of the reconstructed-halo sample. We show that the dominant reconstruction-induced systematics can be described and incorporated within the standard EFT framework. In particular, a simple multipole-dependent rescaling inferred directly from the data on large scales captures the dominant effect, while residual small-scale changes are absorbed by the standard counterterm and stochastic sector, without introducing additional reconstruction-specific parameters. The reconstructed-halo sample yields unbiased constraints on cosmological parameters, including the growth rate $fσ_8$ and Alcock-Paczynski parameters. Compared to the galaxy sample, it enables both improved robustness and increased statistical precision: the inferred $fσ_8$ remains stable when extending the fit beyond $k_{\max}\simeq 0.2\,h\,{\rm Mpc}^{-1}$, with its uncertainty reduced by more than $20\%$.

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arXiv2026

Imprints of gravitational-wave polarizations on projected tidal tensor in three dimensions

Gravitational waves (GWs) distort galaxy shapes through the tidal effect, offering a novel avenue to probe the nature of gravity. In this paper, we investigate how extra GW polarizations beyond those predicted by general relativity imprint observable signatures on galaxy shapes. Since galaxy shapes are measured as two-dimensional images projected onto the celestial sphere, we present three-dimensional statistical quantities of the projected tidal tensor sourced by the tensor perturbation. We show that the presence of extra polarization modes modifies both the amplitude and angular dependence of the correlation functions. Furthermore, we identify a distinct observational channel for probing parity violation in helicity-two and helicity-one modes. In particular, we show that if they propagate at different speeds, galaxy surveys can disentangle the source of parity violation. Our findings establish a theoretical framework for using upcoming large-scale galaxy surveys to test modified gravity theories through the polarization content of GWs.

astro-ph.CO↗

arXiv2026

Large-scale halo velocity correlations and the impact of finite simulation volumes

The velocity correlation functions directly measured from the peculiar velocity field of dark matter in numerical simulations are known to have an amplitude lower than that predicted by theoretical models at large scales. The trend persists for dark-matter halos or galaxies that are more closely related to the observables. We investigate the impact of the finite simulation box sizes on the measured velocity correlation functions of halos, utilizing N-body simulations with different box sizes. We measure the halo velocity correlations from N-body simulations with side lengths of $1{\rm Gpc}/h$ and $2{\rm Gpc}/h$, confirming the former is more suppressed compared to the linear theory prediction on large scales due to the lack of large-scale modes beyond the box size. In contrast, even though we subdivide the larger-box simulations into those with side lengths of $1{\rm Gpc}/h$, the amount of the suppression is the same as that from the original boxes, as the large-scale modes are already imprinted. Introducing the lower limit of the integral in the Hankel transform, $k_{\rm min}$, as a free parameter and marginalizing it over, we find that the constrained growth rate parameter, $f(z)σ_8(z)$, returns the correct value assumed in the simulations. However, when we ignore the effect and set $k_{\rm min}=0$, the constraint on $fσ_8$ is significantly biased if the correlation between different separation bins is also ignored. Furthermore, we find that the suppression of the velocity correlation amplitude on large scales depends on halo mass, with more massive halos exhibiting a systematically stronger suppression. These results highlight the importance of accounting for missing long-wavelength modes when developing simulation-based modeling of velocity statistics, such as emulators.

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arXiv2025

Galaxy Spin Alignment with Tidal Fields in the SDSS-IV MaNGA Survey

The tidal torque theory (TTT) predicts that galaxy spins are correlated with the surrounding tidal field, reflecting how angular momentum is acquired during structure formation. We present a new observational test of this prediction using the final data release of the Sloan Digital Sky Survey IV Mapping Nearby Galaxies at Apache Point Observatory integral field spectroscopy survey, which enables direct spin measurements from stellar and ionized gas kinematics for a sample of 6325 disk galaxies. We utilize the three-dimensional tidal field reconstructed from the galaxy distribution, providing a physically defined reference frame for the analysis. We find that massive galaxies tend to align their spins parallel to the intermediate axis of the tidal field, consistent with the prediction of the TTT, while also showing a tendency to align perpendicular to the major axis. In contrast, low-mass galaxies exhibit the opposite trend, with a transition mass of $M_* \sim 10^{10}-10^{10.5}M_\odot$. No significant alignment is detected with respect to the minor axis across all stellar masses. We further examine the dependence on morphology and environment, finding that S0 and early-type spiral galaxies exhibit stronger alignment signals than late-type spirals. The alignment trend becomes particularly pronounced in regions of high tidal anisotropy and high overdensity. A mutual information analysis identifies these environmental factors as the dominant drivers of the observed trends. Our results provide new empirical evidence for the connection between galaxy spins and the cosmic tidal field.

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arXiv2025

Cosmological constraints on nonphantom dynamical dark energy with DESI Data Release 2 Baryon Acoustic Oscillations: A 3$σ$+ lensing anomaly

We consider a 12-parameter cosmological model with non-phantom dynamical dark energy (NPDDE), where non-phantom implies that the equation of state (EoS) of dark energy (DE), $w(z)\geq-1$ for all redshifts $z$. Thus, the DE EoS covers the parameter space corresponding to the popular single scalar-field dark energy models, i.e., Quintessence. The cosmological model comprises 6 parameters of the $Λ$-Cold Dark Matter ($Λ$CDM) model, and additionally the dynamical DE EoS parameters ($w_0$, $w_a$), the scaling of the lensing amplitude ($A_{\rm lens}$), sum of the neutrino masses ($\sum m_ν$), the effective number of non-photon relativistic degrees of freedom ($N_{\rm eff}$), and the running of the scalar spectral index ($α_s$). We derive constraints on the parameters by combining the latest Dark Energy Spectroscopic Instrument (DESI) Data Release (DR) 2 Baryon Acoustic Oscillation (BAO) measurements with cosmic microwave background (CMB) power spectra from Planck Public Release (PR) 4, CMB lensing data from Planck PR4 and Atacama Cosmology Telescope (ACT) DR6, uncalibrated Type Ia supernovae (SNe) data from the Pantheon+ and Dark Energy Survey (DES) Year 5 (DESY5) samples, and Weak Lensing (WL) data from DES Year 1. Our major finding is that with CMB+BAO+WL and CMB+BAO+SNe+WL, we find 3$σ$+ evidence for $A_{\rm lens} >1$, indicating a higher than expected CMB lensing amplitude relative to the NPDDE prediction of unity. This implies that for cosmology to accommodate realistic quintessence-like dark energy models (as opposed to unrealistic phantom DE), one would also need to explain a relatively significant presence of the lensing anomaly.

astro-ph.CO↗

arXiv2025

Evidence for Intrinsic Galaxy Alignments in Ellipticity Autocorrelations out to $100 h^{-1}\textrm{Mpc}$ from SDSS Galaxies with DESI Imaging

Measuring the autocorrelation of galaxy shapes, known as the intrinsic-intrinsic (II) correlation, is important for both cosmology and understanding the formation of massive elliptical galaxies. However, such measurements are significantly more challenging than those of the cross-correlation with galaxy density (GI correlation) due to the much lower signal-to-noise ratio. In this Letter, we report the first observational evidence for large-scale intrinsic alignments measured from the ellipticity autocorrelations, extending out to $100\,h^{-1}\,{\rm Mpc}$. From the Sloan Digital Sky Survey (SDSS) and SDSS-III Baryon Oscillation Spectroscopic Survey, we analyze, over the redshift range $0.16\leq z\leq 0.70$, luminous red galaxy, LOWZ, and CMASS galaxy samples, the latter two of which are crossmatched with high-quality Dark Energy Spectrograph Instrument imaging data. By expanding one of the two II correlation functions, II($-$), in terms of the associated Legendre polynomials, we effectively isolate the line-of-sight projection effects and enhance the signal. The resulting correlation for all three samples exhibits a clear power-law form. We also show that jointly analyzing the two II correlations, II($+$) and II($-$), increases the detection significance by $\sim 10\%$, even though both are derived from the same $E$-mode power spectrum. Importantly, this measurement opens a new observational window for probing signals uniquely encoded in shape autocorrelations, such as tensor perturbations from the gravitational waves. Our analysis establishes a practical framework for extracting such effects.

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arXiv2025

Probing vector chirality in the early Universe

We explore the potential of using late-time galaxy spins to test the parity symmetry of primordial vector fossils. Using $N$-body simulations, we analyze halo spins as a reliable proxy for galaxy spins to investigate the detectability of this effect. We develop a novel approach to generate initial conditions (ICs) that have substantial parity asymmetry but do not alter the initial matter power spectrum. We construct the initial spin fields from the parity broken ICs and halo spin fields using late-time halos evolved from such ICs. Focusing on the helicity of these vector fields, we detect substantial asymmetry in the initial spin field. In addition, we find that over $50\%$ of the initial spin field's asymmetry remains in the late-time halo spin field on a range of scales. Based on mock galaxy spin fields derived from the halo spin fields, we forecast that a maximum detection at $13σ$ is possible with the final DESI BGS for the model considered in this analysis. Our findings demonstrate that primordial vectorial parity violation survives nonlinear gravitational evolution, and thus, can be effectively probed with galaxy spins at late times.

astro-ph.CO↗

arXiv2025

Constraining cosmology with N-body simulations for future spectroscopic galaxy surveys at $2\leq z\leq 3$

Determining the spatial curvature ($Ω_k$) independent of cosmic microwave background observations plays a key role in revealing the physics of the early universe. The Hubble tension is one of the most serious issues in modern cosmology. We investigate halo catalogs identified from $N$-body simulations at $z=2$ and 3, mimicking high-redshift galaxy surveys. We measure redshift-space correlation functions of halos from the two snapshots. We detect clear features of baryon acoustic oscillations and redshift-space distortions. We find that we can obtain a few percent constraints on both the geometric distances and growth of structure at the distant universe in future surveys. By taking into account the information of the underlying matter power spectrum, we demonstrate that we can also achieve constraint on the Hubble constant $H_0$ with a few percent as well as the spatial curvature with $|Ω_k|\lesssim 0.1$ by observing galaxies with the number density with $\bar{n}_{\rm g}\simeq 10^{-4} (~h^3{\rm ~Mpc}^{-3})$. Our analysis provides a timely forecast for the upcoming spectroscopic surveys, which target emission line galaxy or dusty star-forming galaxy samples.

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arXiv2025

Improving cosmological constraints via galaxy intrinsic alignment in full-shape analysis

The intrinsic alignment (IA) of galaxy shapes probes the underlying gravitational tidal field, thus offering cosmological information complementary to galaxy clustering. In this paper, we perform a Fisher forecast to assess the benefit of IA in improving cosmological parameter constraints, for the first time, leveraging the full-shape (FS) information of IA statistics. Our forecast is based on PFS-like and Euclid-like surveys as examples of deep and wide galaxy surveys, respectively. We explore various cosmological models, with the most comprehensive one simultaneously including dynamical dark energy, curvature, massive neutrinos, and modified gravity (MG). We find that adding FS IA information significantly tightens cosmological constraints relative to the FS clustering-only cases, particularly for dynamical dark energy and nonflat-MG models. For a deep galaxy survey, the Figure-of-Merit for the dark energy equation of state parameters is improved by at least more than $40\%$ in all dynamical dark energy models investigated. For nonflat-MG models, parameter constraints are tightened by $6-28\%$, except for the dark matter density and spectral index parameters. For a wide galaxy survey, improvements with IA become milder, although its joint constraints are tighter than those from the deep survey. Our findings highlight the efficacy of the galaxy IA as a complementary cosmological probe to galaxy clustering.

astro-ph.CO↗

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

First confirmation of anisotropic halo bias from statistically anisotropic matter distributions

We confirm for the first time the existence of distinctive halo bias associated with the quadrupolar type of statistical anisotropy (SA) of the linear matter density field using cosmological $N$-body simulations. We find that the coefficient of the SA-induced bias for cluster-sized halos takes negative values and exhibits a decreasing trend with increasing halo mass. This results in the quadrupole halo power spectra in a statistically anisotropic universe being less amplified compared to the monopole spectra. The anisotropic feature in halo bias that we found presents a promising new tool for testing the hypothesis of a statistically anisotropic universe, with significant implications for the precise verification of anisotropic inflation scenarios and vector dark matter and dark energy models.

astro-ph.CO↗

arXiv2025

Squeezing Full-Shape Dynamical Dark Energy Constraints with Galaxy Alignments

Recent $2-4σ$ deviations from the Cosmological Constant $Λ$ suggest that dark energy (DE) may be dynamical, based on baryon acoustic oscillations and full-shape galaxy clustering (FS GC) analyses. This calls for even tighter DE constraints to narrow down its true nature. In this Letter, we explore how galaxy intrinsic alignments (IA) can enhance the FS GC-based DE constraints, using Fisher forecasts on various extensions of dynamical DE models, including scenarios with curvature, massive neutrinos, and modified gravity. Incorporating IA improves the DE Figure-of-Merit by $42-57\%$ and tightens the primordial power spectrum amplitude constraints by $17-19\%$. Our findings highlight IA's potential as a valuable cosmological probe complementary to GC.

astro-ph.CO↗

arXiv2025

SHAPE: cosmology with cluster halo intrinsic alignments from subhalo distributions

Galaxy clusters trace the most massive dark matter haloes, whose shapes and orientations reflect the imprint of the cosmic large-scale tidal field. This paper introduces the Subhalo-based Halo Alignment and Projected Ellipticity (SHAPE) technique, which reconstructs cluster halo shapes from the projected distribution of subhaloes, providing a novel approach to investigate intrinsic alignment (IA) correlations between cluster halo shapes and the surrounding density field. We measure halo shapes and orientations using different line-of-sight projection depths and find that, with modest projection depths, the shapes and orientations recovered by SHAPE show good agreement with those measured directly from the simulation particles. Using these SHAPE-derived shapes, we compute IA correlation functions from N-body simulations in both real and redshift space. The IA correlation multipoles exhibit features consistent with baryon acoustic oscillations around 100 Mpc/h and show redshift-space distortion (RSD) effects that agree well with predictions from a non-linear alignment model incorporating RSD. We further demonstrate that the structure growth rate parameter can be robustly estimated without bias from these IA correlations, providing a new avenue for cosmological parameter estimation. Expanding the IA correlations in an associated Legendre basis yields results consistent with those from the standard Legendre expansion, but with improved statistical significance. These results suggest that SHAPE may enhance cosmological parameter constraints in future galaxy surveys.

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