Planes of satellite galaxies and the cosmic web

TL;DR

This study investigates the alignment of satellite galaxy planes with the cosmic web's shear field, finding general consistency with the { extLambda}CDM model and highlighting the influence of local large-scale structures.

Contribution

It re-examines satellite galaxy planes within the { extLambda}CDM framework using the local shear tensor, showing their alignment with the cosmic web's structure.

Findings

Most satellite planes align with the shear-induced compression axis.

The Local Group and Centaurus A are in a filament influenced by the Virgo cluster.

The Milky Way's satellite plane shows slight misalignment due to tidal effects.

Abstract

Recent observational studies have demonstrated that the majority of satellite galaxies tend to orbit their hosts on highly flattened, vast, possibly co-rotating planes. Two nearly parallel planes of satellites have been confirmed around the M31 galaxy and around the Centaurus A galaxy, while the Milky Way also sports a plane of satellites. It has been argued that such an alignment of satellites on vast planes is unexpected in the standard ({\Lambda}CDM) model of cosmology if not even in contradiction to its generic predictions. Guided by {\Lambda}CDM numerical simulations, which suggest that satellites are channeled towards hosts along the axis of the slowest collapse as dictated by the ambient velocity shear tensor, we re-examine the planes of local satellites systems within the framework of the local shear tensor derived from the Cosmicflows-2 dataset. The analysis reveals that the Local Group and Centaurus A reside in a filament stretched by the Virgo cluster and compressed by the expansion of the Local Void. Four out of five thin planes of satellite galaxies are indeed closely aligned with the axis of compression induced by the Local Void. Being the less massive system, the moderate misalignment of the Milky Way's satellite plane can likely be ascribed to its greater susceptibility to tidal torques, as suggested by numerical simulations. The alignment of satellite systems in the local universe with the ambient shear field is thus in general agreement with predictions of the {\Lambda}CDM model.