The impact of our peculiar motion on primordial non-Gaussianity measurements using the LIGER4GAL framework

TL;DR

This paper introduces an improved LIGER4GAL framework to accurately model relativistic redshift-space distortions in galaxy surveys, assessing their impact on primordial non-Gaussianity measurements.

Contribution

The paper presents an updated implementation of the LIGER method that incorporates all linear-order relativistic RSDs at the tracer level in high-resolution simulations.

Findings

Relativistic effects can bias $f_{nl}$ measurements by over 1 sigma if neglected.

Omission of the observer's peculiar velocity effect can lead to significant biases in PNG estimates.

LIGER4GAL accurately reproduces non-linear clustering and relativistic RSDs on large scales.

Abstract

Current and forthcoming galaxy surveys will map the observable Universe with unprecedented depth, sky coverage, and precision. These maps are affected by relativistic redshift-space distortions (RSDs), which become increasingly relevant on ultra-large scales. Accurate modelling of these relativistic RSDs is essential to avoid systematic biases in key cosmological measurements, such as primordial non-Gaussianity (PNG). To address this, we introduce an updated implementation of the LIGER method, LIGER4GAL, which incorporates all linear-order relativistic RSDs directly at the tracer level of high-resolution N-body simulations. We demonstrate that LIGER4GAL improves upon previous iterations of the LIGER method by reproducing the expected non-linear clustering while maintaining accuracy for relativistic RSDs on large scales. We use the updated code to generate a DESI-like sample of luminous red galaxies from the Huge MultiDark Planck simulation. By measuring the power spectrum multipoles of this sample with and without the imprint of relativistic RSDs, we assess the impact of relativistic effects on measurements of the local PNG signal ($f_\mathrm{nl}$). We find that the omission of the''finger-of-the-observer'' (sourced by the peculiar velocity of the observer) effect in the power spectrum modelling can bias measurements of $f_{\rm nl}$ by more than $1$ ($0.25$) $ \sigma_{f_{\rm nl}}$ in 40% (80%) of the possible realizations of the universe if scales down to $k_\mathrm{min} = 0.0015\,h/\mathrm{Mpc}$ are included.