Galaxy power-spectrum responses and redshift-space super-sample effect

TL;DR

This paper calculates how large-scale density and tidal fluctuations influence galaxy clustering measurements in redshift space, affecting cosmological parameter estimation and survey analysis.

Contribution

It introduces the first computation of redshift-space response functions to long modes, including growth and dilation effects, validated with simulations.

Findings

Long modes cause significant super-sample covariance in galaxy surveys.

Dilation effects shift BAO peaks and impact AP tests.

Long modes influence RSD measurements and survey constraints.

Abstract

As a major source of cosmological information, galaxy clustering is susceptible to long-wavelength density and tidal fluctuations. These long modes modulate the growth and expansion rate of local structures, shifting them in both amplitude and scale. These effects are often named the growth and dilation effects, respectively. In particular the dilation shifts the baryon acoustic oscillation (BAO) peak and breaks the assumption of the Alcock-Paczynski (AP) test. This cannot be removed with reconstruction techniques because the effect originates from long modes outside the survey. In redshift space, the long modes generate a large-scale radial peculiar velocity that affects the redshift-space distortion (RSD) signal. We compute the redshift-space response functions of the galaxy power spectrum to long density and tidal modes at leading order in perturbation theory, including both the growth and dilation terms. We validate these response functions against measurements from simulated galaxy mock catalogs. As one application, long density and tidal modes beyond the scale of a survey correlate various observables leading to an excess error known as the super-sample covariance, and thus weaken their constraining power. We quantify the super-sample effect on BAO, AP, and RSD measurements, and study its impact on current and future surveys.