Biasing phenomenon

TL;DR

This study investigates the biasing phenomenon in galaxy formation by analyzing power spectra and correlation functions of simulated galaxy and dark matter samples, revealing how projection effects influence observed clustering.

Contribution

It introduces a density-based algorithm for selecting simulated galaxies and compares 2D and 3D correlation functions to understand biasing effects.

Findings

2D correlation functions have lower amplitudes than 3D functions due to projection effects.

The bias factor for L* galaxies is estimated at approximately 1.85.

Projection effects cause clusters and filaments to fill in voids, reducing correlation amplitudes.

Abstract

We study biasing as a physical phenomenon by analysing power spectra (PS) and correlation functions (CF) of simulated galaxy samples and dark matter (DM) samples. We apply an algorithm based on the local densities of particles, $\rho$, to form populations of simulated galaxies, using particles with $\rho \ge \rho_0$. We calculate two-point CF of projected (2D) and spatial (3D) density fields of simulated galaxies for various particle-density limits $\rho_0$. We compare 3D and 2D CFs; in 2D case we use samples of various thickness to find the dependence of 2D CFs on thickness of samples. Dominant elements of the cosmic web are clusters and filaments, separated by voids filling most of the volume. In individual 2D sheets positions of clusters and filaments do not coincide. As a result, in projection clusters and filaments fill in 2D voids. This leads to the decrease of amplitudes of CFs in projection. For this reason amplitudes of 2D CFs are lower than amplitudes of 3D CFs, the difference is the larger, the thicker are 2D samples. Using PS and CFs of simulated galaxies and DM we estimate the bias factor for $L^\ast$ galaxies, $b^\ast =1.85 \pm 0.15$.