Alignment of Galaxies with Large Scale Structure

The internal structure of galaxies is strongly affected by the gravitational influence of surrounding matter, on scales up to several megaparsecs. For example, galaxies are tidally torqued by surrounding galaxies and clusters. Conversely, a single massive elliptical galaxy can have a significant gravitational influence on surrounding satellite galaxies. To quantify the interplay between galaxies and surrounding structure on larger scales, we have done a study of the alignment of galaxy images with the surrounding large scale structure, using data from the Sloan Digital Sky Survey (SDSS) Legacy Survey. We find that galaxies have a statistically significant tendency ( > 5 sigma ) to align parallel to the larger scale structure surrounding them, on scales up to 7.5 Mpc. This signal is driven primarily by red galaxies that are more luminous than the sample mean ( M_r < -21 ). Blue galaxies do not have a statistically significant tendency to align with the larger scale structure. Both the lack of alignment for blue disk galaxies and the alignment for red elliptical galaxies provide clues to help us decipher the influence of large scale structure on individual galaxies, and vice versa.