Connecting the cosmic web to the spin of dark haloes: implications for galaxy formation

Abstract

We investigate the alignment of the spin of dark matter haloes relative (i) to the surrounding large-scale filamentary structure, and (ii) to the tidal tensor eigenvectors using the Horizon 4π dark matter simulation which resolves over 43 million dark matter haloes at redshift zero. We detect a clear mass transition: the spin of dark matter haloes above a critical mass M s 0 ≈ 5(±1) × 10 12 M tends to be perpendicular to the closest large-scale filament (with an excess probability of up to 12 per cent), and aligned with the intermediate axis of the tidal tensor (with an excess probability of up to 40 per cent), whereas the spin of low-mass haloes is more likely to be aligned with the closest filament (with an excess probability of up to 15 per cent). Furthermore, this critical mass is redshift-dependent, scaling as M s crit (z) ≈ M s 0 (1 + z) −γ s with γ s = 2.5 ± 0.2. A similar fit for the redshift evolution of the tidal tensor transition mass yields M t 0 ≈ 8(±2) × 10 12 M and γ t = 3 ± 0.3. This critical mass also varies weakly with the scale defining filaments.We propose an interpretation of this signal in terms of large-scale cosmic flows. In this picture, most low-mass haloes are formed through the winding of flows embedded in misaligned walls; hence, they acquire a spin parallel to the axis of the resulting filaments forming at the intersection of these walls. On the other hand, more massive haloes are typically the products of later mergers along such filaments, and thus they acquire a spin perpendicular to this direction when their orbital angular momentum is converted into spin. We show that this scenario is consistent with both measured excess probabilities of alignment with respect to the eigendirections of the tidal tensor, and halo merger histories. On a more qualitative level, it also seems compatible with 3D visualization of the structure of the cosmic web as traced by 'smoothed' dark matter simulations or gas tracer particles. Finally, it provides extra support to the disc-forming paradigm presented by Pichon et al. as it extends it by characterizing the geometry of secondary infall at high redshift.

The Local Group in the Cosmic Web

“…The absence of alignment for the spins is consistent with different studies of spin alingnment that mark the range 10 12 M as either a transition mass from alignment into anti-alignment or from no-alignment into alignment (Hahn et al 2007;Aragón-Calvo et al 2007;Zhang et al 2009;Codis et al 2012;Trowland et al 2013;Libeskind et al 2013;Forero-Romero et al 2014). We refer the reader to Table 2 in Forero-Romero et al (2014) for a review on the different results of spin alignment with the cosmic web in cosmological simulations.…”

The alignment of galaxy spin with the shear field in observations

“…To date, this remains one of the only studies to have done so. Insights from simulations suggest spins align with the eigenvector corresponding to weakest collapse (e3 ) for small haloes and with the eigenvector corresponding to strongest collapse (e1 ) for the most massive haloes (Aragón-Calvo et al 2007;Codis et al 2012;Libeskind et al 2013), although the mechanism that causes this spin flipping is still disputed (Trowland et al 2013). For example, see also .…”

Star formation sustained by gas accretion

“…Pichon et al (2011) carry out simulations where the disk angular momentum comes from filaments and increases over time, building up disks from the inside out. Codis et al (2012), Laigle et al (2013), and Dubois et al (2014) show from cosmological simulations that low-mass galaxies, which tend to be disklike, spin in a direction that is aligned to their accretion filaments, but high-mass spheroidal galaxies spin perpendicular to their filaments. The difference arises because the disks accrete gas directly from their filament and inherit its angular momentum, while the spheroids grow from the mixture of other galaxies coming in along the filament (i.e, grow from mergers).…”