Cosmic Web Type Dependence of Halo Clustering

TL;DR

This study demonstrates that halo clustering varies significantly with cosmic web type, revealing that the web environment influences the bias and distribution of halos across different mass ranges.

Contribution

It introduces a novel classification of halos based on velocity shear eigenvalues and links web type composition to halo clustering behavior across mass scales.

Findings

Node halos show positive bias.

Void and sheet halos are anti-biased.

Web type composition explains mass-dependent clustering.

Abstract

We use the Millennium simulation to show that halo clustering varies significantly with cosmic web type. Halos are classified as node, filament, sheet and void halos based on the eigenvalue decomposition of the velocity shear tensor. The velocity field is sampled by the peculiar velocities of a fixed number of neighbouring halos and spatial derivatives are computed using a kernel borrowed from smoothed particle hydrodynamics. The classification scheme is used to examine the clustering of halos as a function of web type for halos with masses larger than $10^{11}$. We find that node halos show positive bias, filament halos show negligible bias, and void and sheet halos are anti-biased independent of halo mass. Our findings suggest that the mass dependence of halo clustering is rooted in the composition of web types as a function of halo mass. The substantial fraction of node type halos for halo masses $\gtrsim 2\times10^{13}\,h^{-1}\rm M_\odot$ leads to positive bias. Filament type halos prevail at intermediate masses, $10^{12} - 10^{13}\,h^{-1}\rm M_\odot$, resulting in unbiased clustering. The large contribution of sheet type halos at low halo masses $\lesssim 10^{12}\,h^{-1}\rm M_\odot$ generates anti-biasing.