Beyond boundaries of redshift surveys: assessing mass fluctuations on "super-survey" scales

TL;DR

This paper investigates how large-scale mass fluctuations outside a galaxy survey volume influence observed density fields and redshift space distortions, highlighting potential biases in growth factor estimates.

Contribution

It assesses the impact of super-survey scale mass fluctuations on redshift space distortions and the accuracy of growth factor measurements.

Findings

Super-survey mass fluctuations affect redshift space anisotropies.

Current growth factor estimates may have uncertainties of a few percent due to external mass influences.

Large-scale motions outside survey volumes can bias cosmological inferences.

Abstract

The observed density field in redshift space is directly affected by the radial motions generated from mass fluctuations outside the volume occupied by a given galaxy redshift survey. These motions introduce redshift space anisotropies which are more pronounced at larger distances from the survey's center, thus offering clues to the nature of mass fluctuations on super-survey scales. Furthermore, we note that all estimates of the growth factor derived from redshift space distortions are based on relations which explicitly assume that the velocity field is generated by mass fluctuations inside the survey volume. This may cause uncertainties in these estimates which are on the order of a few percent.