Large Scale Limit of the Observed Galaxy Power Spectrum

TL;DR

This paper estimates relativistic effects on the observed galaxy power spectrum, showing they can mimic primordial signals but are manageable for current surveys and relevant for future ones.

Contribution

It provides the first consistent estimate of relativistic effects in the galaxy power spectrum and clarifies their distinction from primordial non-Gaussianities.

Findings

Relativistic effects can account for up to 10% of the observed power spectrum.

Effects with similar scale dependence to primordial signals are negligible for current surveys.

Relativistic effects will become significant for future large-scale galaxy observations.

Abstract

The large scale limit of the galaxy power spectrum provides a unique window into the early Universe through a possible detection of scale dependent bias produced by primordial non Gaussianities. On such large scales, relativistic effects could become important and be confused for a primordial signal. In this Letter we provide the first consistent estimate of such effects in the observed galaxy power spectrum, and discuss their possible degeneracy with local primordial non Gaussianities. We also clarify the physical differences between the two signatures, as revealed by their different sensitivity to the large scale gravitational potential. Our results indicate that, while relativistic effects could easily account for 10% of the observed power spectrum, the subset of those with a similar scale dependence to a primordial signal can be safely ignored for current galaxy surveys, but it will become relevant for future observational programs.