We explore the characteristics of the cosmic web around Local-Group (LG)-like pairs using a cosmological simulation in the ΛCDM cosmology. We use the Hessian of the gravitational potential to classify regions on scales of ∼2 Mpc as a peak, sheet, filament, or void. The sample of LG counterparts is represented by two samples of halo pairs. The first is a general sample composed of pairs with similar masses and isolation criteria as observed for the LG. The second is a subset with additional observed kinematic constraints such as relative pair velocity and separation. We find that the pairs in the LG sample with all constraints are: (1) preferentially located in filaments and sheets, (2) located in a narrow range of local overdensity 0 < δ < 2, web ellipticity 0.1 < e < 1.0, and prolateness −0.4 < p < 0.4, (3) strongly aligned with the cosmic web. The alignments are such that the pair orbital angular momentum tends to be perpendicular to the smallest tidal eigenvector, , which lies along the filament direction or the sheet plane. A stronger alignment is present for the vector linking the two halos with the vector . Additionally, we fail to find a strong correlation between the spin of each halo in the pair with the cosmic web. All of these trends are expected to a great extent from the selection of LG total mass in the general sample. Applied to the observed LG, there is a potential conflict between the alignments of the different satellite planes and the numerical evidence for satellite accretion along filaments; the direction defined by . This highlights the relevance of achieving a precise characterization for the location of the LG in the cosmic web in the cosmological context provided by ΛCDM.
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Forero-Romero et al. (2015) studied this question.