Detecting Galaxy-Filament Alignments in the Sloan Digital Sky Survey III

TL;DR

This study detects statistically significant galaxy alignments with cosmic filaments in the Sloan Digital Sky Survey, revealing that galaxy properties influence the strength of these alignments over large scales.

Contribution

It provides the first evidence of galaxy-filament alignments in SDSS data and shows how galaxy properties affect the alignment strength.

Findings

Galaxies align with nearby filaments over 30-40 Mpc.

Bright, early-forming galaxies show stronger alignment.

Alignment is present even without nearby galaxy clusters.

Abstract

Previous studies have shown the filamentary structures in the cosmic web influence the alignments of nearby galaxies. We study this effect in the LOWZ sample of the Sloan Digital Sky Survey using the "Cosmic Web Reconstruction" filament catalogue. We find that LOWZ galaxies exhibit a small but statistically significant alignment in the direction parallel to the orientation of nearby filaments. This effect is detectable even in the absence of nearby galaxy clusters, which suggests it is an effect from the matter distribution in the filament. A nonparametric regression model suggests that the alignment effect with filaments extends over separations of 30-40 Mpc. We find that galaxies that are bright and early-forming align more strongly with the directions of nearby filaments than those that are faint and late-forming; however, trends with stellar mass are less statistically significant, within the narrow range of stellar mass of this sample.