Kinematic Bias in Cosmological Distance Measurement

TL;DR

This paper explains biases in cosmological distance measurements at low redshift as a simple kinematic Malmquist-like bias, clarifying its relation to small-scale velocity effects and correcting previous overestimations.

Contribution

It demonstrates that the observed biases can be understood as a non-relativistic kinematic effect and refines the standard formula for small-scale velocity bias.

Findings

Biases are akin to a Malmquist-like effect in low-redshift cosmology.

Standard formulas overestimate the bias by a factor of two.

The effect is similar to small-scale velocity-induced distance bias.

Abstract

Recent calculations using non-linear relativistic cosmological perturbation theory show biases in the mean luminosity distance and distance modulus at low redshift. We show that these effects may be understood very simply as a non-relativistic, and purely kinematic, Malmquist-like bias, and we describe how the effect changes if one averages over sources that are limited by apparent magnitude. This effect is essentially identical to the distance bias from small-scale random velocities that has previously been considered by astronomers, though we find that the standard formula overestimates the homogeneous bias by a factor 2.