Anisotropy in the matter distribution beyond the baryonic acoustic oscillation scale

TL;DR

This paper demonstrates that matter distribution exhibits anisotropy beyond the BAO scale, affecting BAO measurements, with implications for future galaxy surveys and dark energy detection.

Contribution

It reveals anisotropic matter distribution beyond the BAO scale using N-Body simulations and discusses its impact on BAO peak measurements.

Findings

Correlation functions are enhanced or reduced along peak orientations.

BAO peak shifts depending on measurement direction.

Anisotropy influences observed galaxy correlation functions.

Abstract

Tracing the cosmic evolution of the Baryonic Acoustic Oscillation (BAO) scale with galaxy two point correlation functions is currently the most promising approach to detect dark energy at early times. A number of ongoing and future experiments will measure the BAO peak with unprecedented accuracy. We show based on a set of N-Body simulations that the matter distribution is anisotropic out to ~150 Mpc/h, far beyond the BAO scale of ~100M pc/h, and discuss implications for the measurement of the BAO. To that purpose we use alignment correlation functions, i.e., cross correlation functions between high density peaks and the overall matter distribution measured along the orientation of the peaks and perpendicular to it. The correlation function measured along (perpendicular to) the orientation of high density peaks is enhanced (reduced) by a factor of ~2 compared to the conventional correlation function and the location of the BAO peak shifts towards smaller (larger) scales if measured along (perpendicular to) the orientation of the high density peaks. Similar effects are expected to shape observed galaxy correlation functions at BAO scales.