Wobbling Galaxy Spin Axes in Dense Environments

Abstract

The orientation of galaxy spin vectors within the large scale structure has been considered an important test of our understanding of structure formation. We investigate the angular changes of galaxy spin vectors in clusters -denser environments than are normally focused upon, using hydrodynamic zoomed simulations of 17 clusters YZiCS and a set of complementary controlled simulations. The magnitude by which galaxies change their spin vector is found to be a function of their rotational support with larger cumulative angular changes of spin vectors when they have initially lower V θ /σ. We find that both mergers and tidal perturbations can significantly swing spin vectors, with larger changes in spin vector for smaller pericentre distances. Strong tidal perturbations are also correlated with the changes in stellar mass and specific angular momentum of satellite galaxies. However, changes in spin vector can often result in a canceling out of previous changes. As a result, the integrated angular change is always much larger than the angular change measured at any instant. Also, overall the majority of satellite galaxies do not undergo mergers or sufficiently strong tidal perturbation after infall into clusters, and thus they end up suffering little change to their spin vectors. Taken as a whole, these results suggest that any signatures of spin alignment from the large scale structure will be preserved in the cluster environment for many gigayears.

The SAMI Galaxy Survey: Kinematic Alignments of Early-type Galaxies in A119 and A168

“…Both tests give a probability of <0.01, so the null hypothesis of no difference is rejected. On the other hand, the alignment signal for galaxies closer to the cluster center (R1 in Figure 5, light green histograms and the solid line PDF) does not disappear completely, but it is considerably weakened, as can be expected from the results of Lee et al (2018).…”

“…According to Lee et al (2018), cluster environments do not efficiently re-orient galaxy spin vectors unless a merger or strong tidal perturbation was encountered. Nevertheless, the change in the spin axis tends to increase with time after infall of a galaxy into the cluster, regardless of mergers (see panel (d) of Figure 5 of Lee et al 2018).…”

“…According to Lee et al (2018), cluster environments do not efficiently re-orient galaxy spin vectors unless a merger or strong tidal perturbation was encountered. Nevertheless, the change in the spin axis tends to increase with time after infall of a galaxy into the cluster, regardless of mergers (see panel (d) of Figure 5 of Lee et al 2018). We, therefore, divide the sample into two subsamples based on the distribution of the population for a particular time since infall, in a projected phase-space diagram from Rhee et al (2017, Figure 6), as shown in Figure 5: (1) galaxies in R1 (light green circles, 73 galaxies found in the projected phase-space region that is dominated by ancient infallers) and (2) galaxies in R2 (sky blue circles, 60 galaxies in the region dominated by infalling populations).…”

“…Recently, Kim et al (2018) found a clear alignment for the Virgo early-type galaxies using stellar kinematic position angles (PA kin ) from ATLAS 3D . Moreover, according to Lee et al (2018), who performed an analysis on the YZiCS cluster simulations (Choi & Yi 2017), a galaxy spin axis acquired within a large-scale structure can be preserved for many gigayears, even after entering a cluster.…”

Mysterious Coherence in Several-megaparsec Scales between Galaxy Rotation and Neighbor Motion

“…Finally, we try to reconcile this scenario with the previous findings that the spin axes of galaxies are aligned with large-scale filaments. According to recent studies in simulations (Navarro et al 2004;Aragón-Calvo et al 2007;Brunino et al 2007;Cen 2014;Dubois et al 2014;Liu 2017;Lee et al 2018) and in observations (Tempel & Libeskind 2013;Zhang et al 2013Zhang et al , 2015Hirv et al 2017;Kim et al 2018;Jeong et al 2019), late-type galaxies in a filament tend to have spin axes parallel with the filament direction, while spin axes of early-type galaxies tend to be perpendicular to it. Since the galaxies with strong coherence signals in our results may be mainly late-type galaxies, if they are located in filaments, their spin axes may be aligned to be parallel with filaments according to those studies.…”