# Anisotropic halo assembly bias and redshift-space distortions

## TL;DR

This paper investigates how large-scale tidal fields influence halo properties and induce anisotropic clustering effects that can bias cosmological parameter estimates from redshift-space observations.

## Contribution

It demonstrates the significant impact of anisotropic assembly bias on halo clustering and redshift-space distortions, revealing potential contamination in cosmological measurements.

## Key findings

- Large-scale tidal fields correlate with halo shapes, velocity dispersion, and angular momentum.
- Selection effects linked to these properties can produce anisotropic clustering similar to RSD.
- Redshift-space halo clustering deviates from standard linear RSD models due to anisotropic assembly bias.

## Abstract

We study the effect of large-scale tidal fields on internal halo properties using a set of N-body simulations. We measure significant cross-correlations between large-scale tidal fields and several non-scalar halo properties: shapes, velocity dispersion, and angular momentum. Selection effects that couple to these non-scalar halo properties can produce anisotropic clustering even in real-space. We investigate the size of this effect and show that it can produce a non-zero quadrupole similar in size to the one generated by linear redshift-space distortions (RSD). Finally, we investigate the clustering properties of halos identified in redshift-space and find enormous deviations from the standard linear RSD model, again caused by anisotropic assembly bias. These effects could contaminate the values of cosmological parameters inferred from the observed redshift-space clustering of galaxies, groups, or 21cm emission from atomic hydrogen, if their selection depends on properties affected by halo assembly bias. We briefly discuss ways in which this effect can be measured in existing and future large-scale structure surveys.