# Galaxy Group Spin Alignment with Cosmic Filament in the TNG Simulation

## TL;DR

This study uses the TNG300-1 simulation to analyze how galaxy group spins align with cosmic filaments, revealing a perpendicular alignment influenced mainly by group mass and proximity to filaments.

## Contribution

It provides the first systematic analysis of galaxy group spin-filament alignment in a large cosmological hydrodynamical simulation, highlighting key factors affecting this alignment.

## Key findings

- Robust perpendicular alignment between group spin and filament axes.
- Stronger alignment for more massive groups and those closer to filaments.
- Member galaxy-based spin measurements are biased by about 38 degrees.

## Abstract

We investigate the alignment between the spin vectors of galaxy groups and the axes of their nearest cosmic filaments using the TNG300-1 cosmological hydrodynamical simulation. By systematically analyzing a large sample of groups, we find a robust perpendicular alignment between group spin and filament orientation. Among all examined properties, only group mass and the distance to the nearest filament significantly affect the strength of this alignment: more massive groups and those closer to filaments exhibit a stronger perpendicular signal. In contrast, the alignment is largely insensitive to group richness, the stellar mass threshold used to select member galaxies, and redshift. We further quantify the bias introduced by using member galaxies as tracers of group spin, finding a typical misalignment angle of $\sim38^\circ$ between the spin measured from all dark matter particles and that inferred from member galaxies, independent of group richness or stellar mass cut. Our results provide a clear theoretical benchmark for interpreting observational measurements of spin-filament alignment and highlight the importance of considering group mass and environment. These findings help clarify the main factors influencing spin-filament alignment and provide useful context for future observational and theoretical studies of angular momentum in the cosmic web.