Investigating Galaxy-Filament Alignments in Hydrodynamic Simulations using Density Ridges

TL;DR

This study uses hydrodynamic simulations to analyze galaxy-filament alignments, revealing that galaxy orientation correlates with filament proximity and mass, and that filament structures are consistent across galaxy and dark matter reconstructions.

Contribution

It introduces a method to compare galaxy and dark matter filament reconstructions and quantifies galaxy alignment dependence on proximity and subhalo mass.

Findings

Galaxy filaments reconstructed from galaxies closely match those from dark matter.

Galaxy alignment with filaments depends on subhalo mass and proximity.

Galaxies near filaments tend to be rounder than those farther away.

Abstract

In this paper, we study the filamentary structures and the galaxy alignment along filaments at redshift $z=0.06$ in the MassiveBlack-II simulation, a state-of-the-art, high-resolution hydrodynamical cosmological simulation which includes stellar and AGN feedback in a volume of (100 Mpc$/h$)$^3$. The filaments are constructed using the subspace constrained mean shift (SCMS; Ozertem & Erdogmus (2011) and Chen et al. (2015a)). First, we show that reconstructed filaments using galaxies and reconstructed filaments using dark matter particles are similar to each other; over $50\%$ of the points on the galaxy filaments have a corresponding point on the dark matter filaments within distance $0.13$ Mpc$/h$ (and vice versa) and this distance is even smaller at high-density regions. Second, we observe the alignment of the major principal axis of a galaxy with respect to the orientation of its nearest filament and detect a $2.5$ Mpc$/h$ critical radius for filament's influence on the alignment when the subhalo mass of this galaxy is between $10^9M_\odot/h$ and $10^{12}M_\odot/h$. Moreover, we find the alignment signal to increase significantly with the subhalo mass. Third, when a galaxy is close to filaments (less than $0.25$ Mpc$/h$), the galaxy alignment toward the nearest galaxy group depends on the galaxy subhalo mass. Finally, we find that galaxies close to filaments or groups tend to be rounder than those away from filaments or groups.