Abstract
A large-scale hydrodynamical cosmological simulation, Horizon-AGN, is used to
investigate the alignment between the spin of galaxies and the large-scale
cosmic filaments above redshift one. The analysis of more than 150 000 galaxies
with morphological diversity in a 100 Mpc/h comoving box size shows that the
spin of low-mass, rotation-dominated, blue, star-forming galaxies is
preferentially aligned with their neighbouring filaments. High-mass,
dispersion-dominated, red, quiescent galaxies tend to have a spin perpendicular
to nearby filaments. The reorientation of the spin of massive galaxies is
provided by galaxy mergers which are significant in the mass build up of
high-mass galaxies. We find that the stellar mass transition from alignment to
misalignment happens around 3.10^10 M_sun. This is consistent with earlier
findings of a dark matter mass transition for the orientation of the spin of
halos (5.10^11 M_sun at the same redshift from Codis et al., 2012). With these
numerical evidence, we advocate a scenario in which galaxies form in the
vorticity-rich neighbourhood of filaments, and migrate towards the nodes of the
cosmic web as they convert their orbital angular momentum into spin. The
signature of this process can be traced to the physical and morphological
properties of galaxies, as measured relative to the cosmic web. We argue that a
strong source of feedback such as Active Galactic Nuclei is mandatory to quench
in situ star formation in massive galaxies. It allows mergers to play their key
role by reducing post-merger gas inflows and, therefore, keeping galaxy spins
misaligned with cosmic filaments. It also promotes diversity amongst galaxy
properties.
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