A Relativistic Interpretation of Bias in Newtonian Simulations

TL;DR

This paper connects Newtonian simulation bias with relativistic effects, showing that radiation and GR corrections induce scale-dependent bias observable in large-scale cosmic surveys.

Contribution

It introduces a method to interpret Newtonian simulation bias within the weak-field limit of General Relativity, accounting for radiation effects.

Findings

Relativistic bias becomes scale-dependent due to radiation and GR corrections.

The methodology recovers permille-level agreement with relativistic bias calculations in spherical collapse.

Scale-dependent bias could be observed in upcoming large-scale surveys.

Abstract

Observables of cosmic structures are usually not the underlying matter field but biased tracers of matter, such as galaxies or halos. We show how the bias found in Newtonian N-body simulations can be interpreted in terms of the weak-field limit of General Relativity (GR). For this we employ standard Newtonian simulations of cold dark matter and incorporate GR/radiation via a weak-field dictionary that we have recently developed. We find that even when a simple local biasing scheme is employed in the Newtonian simulation, the relativistic bias becomes inherently scale-dependent due to the presence of radiation and GR corrections. This scale-dependence could be in principle observed on large scales in upcoming surveys. As a working example, we apply our methodology to Newtonian simulations for the spherical collapse and recover permille-level agreement between the approaches for extracting the relativistic bias on all considered scales.