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Animations. a very small subset of skeletons at different redshifts extracted from the Horizon 4π simulation, together with unit vectors showing the orientation of the spin of the corresponding dark matter halo with a mass above the transition mass. The spin is indeed perpendicular to the filament for these massive haloes. time sequence evolution of gas tracer particles trapped in walls and filaments and coalescing to form a central galaxy. and same as from another projection. gas tracer particles around a forming galaxy; the ribbon-like filamentary structure feeding the central galaxy is clearly visible on this circular view. the time line of a set of tracer particles is shown; each tracer particle is colour coded with a different colour. First the viewer rotates around the large-scale distribution of the time line tracer particle; later only the inner region and late times are shown. tracking in towards a set of filaments, colour coded by tracer particle density at high redshift. The coplanar distribution of filaments is clearly seen, together with young galaxies which tend to sit perpendicular to the filament axes. The cold gas describes ribbons corresponding to the locus of the shocks which feed these young galaxies. same tracking in at some intermediate redshift; some galaxies are in the process of merging. same tracking in at some later redshift; the result of mergers corresponding to galaxies which have a spin perpendicular to the main axes of the filaments. a zoom over the inner region of which illustrates the walls of the large-scale structures, the shock-induced ribbons and a nice example of a galaxy formed with a spin parallel to its filament.

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