Super-sample tidal modes on the celestial sphere

Abstract

The super-sample tidal effect carries information on long-wavelength fluctuations that we cannot measure directly. It arises from the mode-coupling between short-wavelength and long-wavelength perturbations beyond a finite region of a galaxy survey and violates statistical isotropy of observed galaxy power spectra. In this paper, we propose the use of bipolar spherical harmonic (BipoSH) decomposition formalism to characterize statistically anisotropic power spectra. Using the BipoSH formalism, we perform a comprehensive study of the effect of the super-sample tides on measurements of other cosmological distortions such as the redshift-space distortion (RSD) and Alcock-Paczyński (AP) effects by means of the Fisher information matrix formalism. We find that the BipoSH formalism can break parameter degeneracies among the super-sample tidal, RSD and AP effects, indicating that the super-sample tides have little impact on the measurements of the RSD and AP effects. We also show that the super-sample tides are detectable with an accuracy better than the ΛCDM prediction without impairing the accuracy of measurements of other anisotropies assuming a SPHEREx-like galaxy survey.

Lagrangian approach to super-sample effects on biased tracers at field level: galaxy density fields and intrinsic alignments

“…The expression given above is one of the new results in this paper. The result at the field level consistently reproduces the power spectrum responses to the super-sample modes known in previous works (e.g., [11,12,15,49]). For the sake of the completeness, in Appendix B, we present the derivation of the power spectrum expression based on Eq.…”

“…Then, the covariance matrix of the power spectrum is modified, and the off-diagonal components of the covariance appear non-vanishing, on top of the so-called non-Gaussian covariance, which is induced by the mode coupling due to the small-scale gravitational clustering. There has been numerous works investigating the impact of super-sample modes on the observed LSS and cosmological parameter estimation [5,[8][9][10][11][12][13][14][15][16][17]. However, most of these works has focused on the statistical quantities based on the Eulerian perturbation theory, and considered the power spectrum and its covariance.…”

Large-scale dark matter simulations

“…Hence, when an ensemble of simulations is considered, the variance of modes k\k 0 is zero despite all of them having different initial white noise fields and providing fair ensemble averages for modes k 0 .k.k Ny . This implies that the component of the covariance that is due to large-scale overdensities and tides is underestimated (Akitsu et al 2019) which is sometimes referred to as super-sample covariance-in analogy to a similar effect present in galaxy surveys (Li et al 2018)-, and can be an important source of error in covariance matrices derived from ensembles of simulations, especially if the simulated boxes are of small size (Klypin and Prada 2019). Such effects can be circumvented in ''separate universe'' simulations that are discussed in Sect.…”

Large-scale structure with superhorizon isocurvature dark energy

“…Our analysis contains the effects arising from superhorizon perturbations beyond the horizon. The model may also be interesting when it is investigated with the separate universe simulation method [49][50][51] associated with the viewpoint of the "supersample" mode [52][53][54][55][56], where the effects of the fluctuations with wavelength scales beyond the survey volume/region were investigated and discussed. By using simulations that are compatible with our model, we expect to find more clues to understand the small-scale growth in proportion to k 2 in the nonlinear regime of density perturbations.…”