Observed and simulated galaxies exhibit a significant variation in their
velocity dispersion profiles. We examine the inner and outer slopes of stellar
velocity dispersion profiles using integral field spectroscopy data and compare
them with cosmological hydrodynamic simulations. The simulated galaxies closely
reproduce the variety of velocity dispersion profiles and stellar mass
dependence of both inner and outer slopes as observed. The inner slopes are
mainly influenced by the relative radial distribution of the young and old
stars formed in-situ: a younger center shows a flatter inner profile. The
presence of accreted (ex-situ) stars has two effects on the velocity dispersion
profiles. First, because they are more dispersed in spatial and velocity
distributions compared to in-situ formed stars, it increases the outer slope of
the velocity dispersion profile. It also causes the velocity anisotropy to be
more radial. More massive galaxies have a higher fraction of stars formed
ex-situ and hence show a higher slope in outer velocity dispersion profile and
a higher degree of radial anisotropy. The diversity in the outer velocity
dispersion profiles reflects the diverse assembly histories among galaxies.Comment: 14 pages, 14 figures, submitted to Ap