Multi-spin stellar velocity maps of the most massive galaxies

We present stellar kinematics of the MUSE Most Massive Galaxies (M3G) Survey, comprising 25 galaxies brighter than -25. 7 mag in the Kₛ band and stellar masses above M_⊙. The galaxies are divided into brightest cluster galaxies (BCGs) and lower-ranked (in brightness) galaxies (non-BCGs) in three rich galaxy clusters within the core of the Shapley Supercluster. We find several velocity maps with rich kinematic structures, including multiple spin reversals within the region encompassing two central effective radii, typically associated with BCGs. Additionally, the majority of the BCGs show rotation around the major axis of the galaxy at least in one of the visible velocity components. These kinematic structures are possible only if galaxies have non-axisymmetric shapes and contain several orbital families with both prograde and retrograde rotations. We argue that such velocity maps provide further evidence that the evolution of very massive galaxies is influenced by, possibly repeated, gas-poor major merging. There are six fast rotators in the M3G sample, and they are all among non-BCGs and typically ranked below the third brightest galaxy in their clusters. Based on the properties of the h₃ Gauss-Hermite moment, fast rotation can be linked to the dominance of prograde rotating short-axis tubes in the orbital distribution. Slow rotators are BCGs or the second or sometimes third brightest galaxies, indicating that the galaxy mass (brightness) is not the only driver of low spin and that the location within the local environment also plays a role. Slow rotators, as evidenced from their multi-spin velocity maps, require more complex orbital structures. Furthermore, some BCGs show kinematic evidence for a secondary component at larger radii, which is likely not in equilibrium with the main galaxy and possibly made of stars accreted from other cluster galaxies. Multi-spin velocity maps, low angular momentum, and additional kinematic components highlight the differences in the evolutionary histories of BCGs (including second-ranked galaxies) and non-BCGs.