Evidence for Quadratic Tidal Tensor Bias from the Halo Bispectrum

TL;DR

This paper provides evidence for quadratic tidal tensor bias in galaxy clustering, showing it influences the bispectrum and varies with halo mass, which impacts modeling for precision cosmology.

Contribution

It demonstrates the presence of quadratic tidal tensor bias in the halo bispectrum and compares Lagrangian and Eulerian bias models, highlighting the need to include these effects in galaxy clustering analyses.

Findings

Non-zero tidal tensor bias coefficient found in simulations

Bias parameters show no scale dependence up to k=0.1 h/Mpc

Tidal effects increase with halo mass

Abstract

The relation between the clustering properties of luminous matter in the form of galaxies and the underlying dark matter distribution is of fundamental importance for the interpretation of ongoing and upcoming galaxy surveys. The so called local bias model, where galaxy density is a function of local matter density, is frequently discussed as a means to infer the matter power spectrum or correlation function from the measured galaxy correlation. However, gravitational evolution generates a term quadratic in the tidal tensor and thus non-local in the density field, even if this term is absent in the initial conditions (Lagrangian space). Because the term is quadratic, it contributes as a loop correction to the power spectrum, so the standard linear bias picture still applies on large scales, however, it contributes at leading order to the bispectrum for which it is significant on all scales. Such a term could also be present in Lagrangian space if halo formation were influenced by the tidal field. We measure the corresponding coupling strengths from the matter-matter-halo bispectrum in numerical simulations and find a non-vanishing coefficient for the tidal tensor term. We find no scale dependence of the bias parameters up to k=0.1 h/Mpc and that the tidal effect is increasing with halo mass. While the Lagrangian bias picture is a better description of our results than the Eulerian bias picture, our results suggest that there might be a tidal tensor bias already in the initial conditions. We also find that the coefficients of the quadratic density term deviate quite strongly from the theoretical predictions based on the spherical collapse model and a universal mass function. Both quadratic density and tidal tensor bias terms must be included in the modeling of galaxy clustering of current and future surveys if one wants to achieve the high precision cosmology promise of these datasets.