Perturbed redshifts from N-body simulations

TL;DR

This paper investigates the relativistic corrections to observed redshifts in N-body simulations, highlighting a previously neglected gauge-dependent term that becomes significant on gigaparsec scales.

Contribution

It identifies and analyzes a correction term in simulated redshifts due to gauge issues, which is often overlooked in Newtonian N-body simulations.

Findings

A correction term proportional to the observed length scale over the Hubble scale was found.

The correction is negligible inside the horizon but significant on gigaparsec scales.

Neglecting this term can lead to inaccuracies in modeling large-scale cosmological observations.

Abstract

In order to keep pace with the increasing data quality of astronomical surveys the observed source redshift has to be modeled beyond the well-known Doppler contribution. In this letter I want to examine the gauge issue that is often glossed over when one assigns a perturbed redshift to simulated data generated with a Newtonian N-body code. A careful analysis reveals the presence of a correction term that has so far been neglected. It is roughly proportional to the observed length scale divided by the Hubble scale and therefore suppressed inside the horizon. However, on gigaparsec scales it can be comparable to the gravitational redshift and hence amounts to an important relativistic effect.