A central velocity dispersion refers to the σ of the interior regions of an extended object, such as a galaxy or cluster.
[2] The Andromeda Galaxy (Messier 31) hosts a SMBH about 10 times larger than our own, and has a σ ≈ 160 km/s.
[3] Groups and clusters of galaxies have more disparate (contrasting in degree) velocity dispersions than smaller objects.
[7] For spiral galaxies, the increase in velocity dispersion in population I stars is a gradual process which likely results from the near-random incidence of momentum exchanges, specifically dynamical friction, between individual stars and large interstellar media (gas and dust clouds) with masses greater than 105 M☉.
[8] Face-on spiral galaxies have a central σ ≲ 90 km/s; slightly more if viewed edge-on.