Alignment of spiral and elliptical galaxies from Siena Galaxy Atlas with filaments

The properties of galaxies are known to have been influenced by the large-scale structures that they inhabit. Theory suggests that galaxies acquire angular momentum during the linear stage of structure formation, and hence predict alignments between the spin of halos and the nearby structures of the cosmic web. In this study, we use the largest catalogue of galaxies publicly available-the Siena Galaxy Atlas-to study the alignment of the spin normals of elliptical and spiral galaxies with filaments constructed by applying the Bisous process on galaxies ( z ≤ 0.2) from SDSS – DR12. Our sample comprises 32 517 disc and 18 955 elliptical galaxies that are within 2 Mpc of any filament spine. We find that the spin normals of elliptical galaxies exhibit a strong perpendicular alignment with respect to the orientation of the host filaments, inconsistent with random distributions by up to ≈13 σ . The spin axis of spiral galaxies shows a much weaker but nonzero alignment signal with their host filaments of ≈2.8 σ when compared with random distribution. These numbers depend on exactly how the significance is measured, as elucidated in the text. Furthermore, the significance of the alignment signal is examined as a function of distance from the filament spine. Spiral galaxies reach a maximum signal between 0.5 and 1 Mpc. elliptical galaxies reach their maximum significance between 0.2 and 0.5 Mpc. We also note that with a tailored selection of galaxies, as a function of both i) distance from the filaments and as a ii) function of absolute luminosity, the alignment significance can be maximized.