Power spectrum of halo intrinsic alignments in simulations

Abstract

We use a suite of N-body simulations to study intrinsic alignments (IA) of halo shapes with the surrounding large-scale structure in the ΛCDM model. For this purpose, we develop a novel method to measure multipole moments of the three-dimensional power spectrum of the E-mode field of halo shapes with the matter/halo distribution, $P_{\delta E}^{(\ell )}(k)$ (or $P^{(\ell )}_{{\rm h}E}$), and those of the auto-power spectrum of the E mode, $P^{(\ell )}_{EE}(k)$, based on the E/B-mode decomposition. The IA power spectra have non-vanishing amplitudes over the linear to nonlinear scales, and the large-scale amplitudes at k ≲ 0.1 h Mpc−1 are related to the matter power spectrum via a constant coefficient (AIA), similar to the linear bias parameter of galaxy or halo density field. We find that the cross- and auto-power spectra PδE and PEE at nonlinear scales, k ≳ 0.1 h Mpc−1, show different k-dependences relative to the matter power spectrum, suggesting a violation of the nonlinear alignment model commonly used to model contaminations of cosmic shear signals. The IA power spectra exhibit baryon acoustic oscillations, and vary with halo samples of different masses, redshifts and cosmological parameters (Ωm, S8). The cumulative signal-to-noise ratio for the IA power spectra is about 60% of that for the halo density power spectrum, where the super-sample covariance is found to give a significant contribution to the total covariance. Thus our results demonstrate that the IA power spectra of galaxy shapes, measured from imaging and spectroscopic surveys for an overlapping area of the sky, can be used to probe the underlying matter power spectrum, the primordial curvature perturbations, and cosmological parameters, in addition to the standard galaxy density power spectrum.

Distinguishing between $Λ$CDM and $f(R)$ gravity models using halo ellipticity correlations in simulations

“…Since the II+ and II− correlation functions are noisier than the GI correlation function, as is known for the ΛCDM case, it is harder to see the difference in the II correlation. Nevertheless, for the monopole and quadrupole one can see the same trend that the amplitude in 𝑓 (𝑅) gravity is smaller than that in ΛCDM, due to the fact that the amplitude of IA, often characterized by 𝑏 𝐾 (see equation 7), is positively correlated with the halo bias (Akitsu et al 2021;Kurita et al 2021); more massive halos tend to be more strongly aligned with the large-scale structure.…”

“…Intrinsic alignment (IA) of galaxy shapes, originally focused as a contaminant to gravitational lensing signals (Croft & Metzler 2000;Heavens et al 2000;Hirata & Seljak 2004;Mandelbaum et al 2006;Hirata et al 2007;Blazek et al 2011;Troxel & Ishak 2015;Tonegawa & Okumura 2021), has been drawing attention as a new dynamical and geometric probe of cosmology (e.g., Chisari & Dvorkin 2013;Okumura et al 2019;Kurita et al 2021;Reischke et al 2021;Okumura & Taruya 2021). However, such a possibility has been explored merely by forecast studies or numerical simulations based on the ΛCDM model.…”

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

“…1), showing that the new method gives a larger σ ∼ 0.4 than that of the usual method, σ ∼ 0.3 as shown in Shi et al (2021). The IA power spectrum between matter density field δ m and E-mode shear field γ E is estimated following the method in Kurita et al (2021):…”

“…To do this we use star-forming galaxies simulated in the IllustrisTNG (Springel et al 2018). We use our method to characterize shapes of the galaxies, and then measure the IA power spectrum based on the method in Kurita et al (2021) (also see Shi et al 2021). To make the realistic predictions, we take into account observational effects (sky background, filter transmission and seeing) when characterizing the galaxy shapes.…”

Tightening geometric and dynamical constraints on dark energy and gravity: galaxy clustering, intrinsic alignment and kinetic Sunyaev-Zel'dovich effect

“…Note that the parameter A IA generally depends on properties of the given galaxy population as well as redshift. The analysis of numerical simulations, however, demonstrated that for fixed galaxy/halo properties, A IA is nearly redshift-independent [102]. We thus treat A IA as a constant throughout this paper.…”