Investigating the Effect of Galaxy Interaction on the Evolution of Spin Alignments

Abstract

An observational evidence for the intrinsic galaxy alignments in isolated spiral pairs is presented. From the catalog of the galaxy groups identified by Tempel et al. in the flux limited galaxy sample of the Sloan Digital Sky Survey Data Release 10, we select those groups consisting only of two spiral galaxies as isolated spiral pairs and investigate if and how strongly the spin axes of their two spiral members are aligned with each other. We detect a 4σ signal of intrinsic spin alignment in the isolated spiral pairs, which leads to the rejection of the null hypothesis at the 99.999% confidence level via the Kolmogorov-Smirnov test. It is also found that those isolated pairs comprising two early-type spiral galaxies exhibit the strongest signal of intrinsic spin alignment while the weakest signal is found from the isolated pairs with two late-type spiral galaxies. We also show that the strength of the alignment signal has a weak dependence on the angular separation distance as well as on the luminosity ratio of the member galaxies. Using the dark matter halos consisting of only two subhalos resolved in the EAGLE hydrodynamic simulations, we repeat the same analysis but fail to find any alignment tendency between the spin angular momentum vectors of the stellar components of the subhalos, which is in tension with the observational result. A couple of possible sources of this newly discovered local anomaly is discussed.