The Cosmic Ballet II: spin alignment of galaxies and haloes with large-scale filaments in the EAGLE simulation

Abstract

We investigate the alignment of galaxies and haloes relative to cosmic web filaments using the EAGLE hydrodynamical simulation. We identify filaments by applying the NEXUS+ method to the mass distribution and the Bisous formalism to the galaxy distribution. Both web finders return similar filamentary structures that are well aligned and that contain comparable galaxy populations. EAGLE haloes have an identical spin alignment with filaments as their counterparts in dark matter only simulations: a complex mass dependent trend with low mass haloes spinning preferentially parallel to and high mass haloes spinning preferentially perpendicular to filaments. In contrast, galaxy spins do not show such a spin transition and have a propensity for perpendicular alignments at all masses, with the degree of alignment being largest for massive galaxies. This result is valid for both NEXUS+ and Bisous filaments. When splitting by morphology, we find that elliptical galaxies show a stronger orthogonal spin-filament alignment than spiral galaxies of similar mass. The same is true of their haloes, with the host haloes of elliptical galaxies having a larger degree of orthogonal alignment than the host haloes of spirals. Due to the misalignment between galaxy shape and spin, galaxy minor axes are oriented differently with filaments than galaxy spins. We find that the galaxies whose minor axis is perpendicular to a filament are much better aligned with their host haloes. This suggests that many of the same physical processes determine both the galaxy-filament and the galaxy-halo alignments.

Dark matter halo shapes in the Auriga simulations

“…The opposite trend of triaxiality in MHD simulation as a function of radius compared to the DMO simulations, together with the twisting effect in some of the halos, seems to suggest that memory of the historical buildup is at most poorly reflected in the shapes at z = 0. The second element to take into account is the effect of the cosmic web (both dark matter and gaseous) on any evolutionary trend (Forero-Romero et al 2014;Borzyszkowski et al 2017;Ganeshaiah Veena et al 2019).…”

CHILES VI: H i and H α observations for z < 0.1 galaxies; probing H i spin alignment with filaments in the cosmic web

“…Dark matter halo spin alignment has received much attention in the past, while studies of galaxy spin alignment have emerged only more recently. The dark matter halo spin flip transition is seen in both dark matter only simulations (Ganeshaiah Veena et al 2018;Wang et al 2018) and most hydrodynamical simulations (Codis et al 2018;Ganeshaiah Veena et al 2019). The case of galaxy spin alignment is less clear.…”

The Sheet of Giants: Unusual properties of the Milky Way’s immediate neighbourhood

“…Theoretically, anisotropy in the large-scale mass distribution is known to correlate with dark matter halo properties (e.g., Codis et al 2015;Ramakrishnan et al 2019), although the main effect may be due to changes in local overdensity (Goh et al 2019) and other environmental factors which only correlate with anisotropy (Mansfield & Kravtsov 2019). The spins of galaxies are expected to correlate with the anisotropy of nearby structures (e.g., Navarro et al 2004;Ganeshaiah Veena et al 2019;Kraljic et al 2019, but see Krolewski et al 2019). Observationally, the orientations of disc galaxies are correlated with the large-scale distribution of their neighbouring galaxies both in the Local Volume (Flin & Godlowski 1986, 1990Navarro et al 2004;Noh & Lee 2006) and in the field (Trujillo et al 2006;Jones et al 2010;Tempel & Libeskind 2013).…”