Cosmic web alignments with the shape, angular momentum and peculiar velocities of dark matter haloes

Abstract

We study the alignment of dark matter haloes with the cosmic web characterized by the tidal and velocity shear fields. We focus on the alignment of their shape, angular momentum and peculiar velocities. We use a cosmological N-body simulation that allows to study dark matter haloes spanning almost five orders of magnitude in mass (10 9 -10 14 ) h −1 M and spatial scales of (0.5-1.0)h −1 Mpc to define the cosmic web. The strongest alignment is measured for halo shape along the smallest tidal eigenvector, e.g. along filaments and walls, with a signal that gets stronger as the halo mass increases. In the case of the velocity shear field only massive haloes > 10 12 h −1 M tend to have their shapes aligned along the largest tidal eigenvector; that is, perpendicular to filaments and walls. For the angular momentum we find alignment signals only for haloes more massive than 10 12 h −1 M both in the tidal and velocity shear fields where the preferences is to be parallel to the middle eigenvector; perpendicular to filaments and parallel to walls. Finally, the peculiar velocities show a strong alignment along the smallest tidal eigenvector for all halo masses; haloes move along filaments and walls. The same alignment is present with the velocity shear, albeit weaker and only for haloes less massive than 10 12 h −1 M . Our results show that the two different algorithms used to define the cosmic web describe different physical aspects of nonlinear collapse and should be used in a complementary way to understand the cosmic web influence on galaxy evolution.

The Local Group in the Cosmic Web

“…This is consistent with recent results that report a strong alignment of halo's peculiar velocities along that direction (Forero-Romero et al 2014).…”

“…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.…”

“…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. It seems that this transition has to do with the changes on the major merger rate as a dark matter halo approaches the 10 12 M mass (Forero-Romero 2009;Codis et al 2012).…”

Galaxy And Mass Assembly (GAMA): the galaxy luminosity function within the cosmic web

“…Cautun, van de Weygaert & Jones 2013 for an overview). Many of these studies have been applied to numerical simulations, finding some promising detection of LSS alignments with filaments (Codis et al 2012;Forero-Romero, Contreras & Padilla 2014). Studies of geometric environments in observational data sets have more often focused on identifying individual structures such as voids or filaments rather than on classifying the global volume.…”

REVEALING THE z ∼ 2.5 COSMIC WEB WITH 3D Lyα FOREST TOMOGRAPHY: A DEFORMATION TENSOR APPROACH

“…Hahn et al 2007;Libeskind et al 2012;Forero-Romero et al 2014). In as much as galaxy properties are determined by Figure 3.…”