The kinematics of young and old stellar populations in nuclear rings of
  MUSE TIMER galaxies
  Studying the stellar kinematics of galaxies is a key tool in the
reconstruction of their evolution. However, the current measurements of the
stellar kinematics are complicated by several factors, including dust
extinction and the presence of multiple stellar populations. We use integral
field spectroscopic data of four galaxies from the TIMER survey to explore and
compare the kinematics measured in different spectral regions that are
sensitive to distinct stellar populations. We derive the line-of-sight velocity
and velocity dispersion of both a young (<2 Gyr) and an old stellar population
from the spectral regions around the H$\beta$ line and the Ca II Triplet. In
addition we obtain colour excess, mean age, and metallicity. We report a
correlation of the colour excess with the difference in the kinematic
parameters of the H$\beta$ line and the Ca II Triplet range, which are
dominated by young and old stellar populations, respectively. Young stellar
populations, located primarily in nuclear rings, have higher velocity
dispersions than old ones. These differences in the rings are typically 10 km/s
in velocity dispersion, but up to a mean value of 24 km/s in the most extreme
case. Trends with age exist in the nuclear rings but are less significant than
those with dust extinction. We report different degrees of correlation of these
trends among the galaxies in the sample, which are related to the size of the
Voronoi bins in their rings. No clear trends for the difference of
line-of-sight velocity are observed. The absence of these trends can be
explained as a consequence of the masking process of the H$\beta$ line during
the kinematic extraction, as confirmed by dedicated simulations. Our study
demonstrates that kinematic differences caused by different stellar populations
can be identified in the central regions of nearby galaxies even from
intermediate resolution spectroscopy.
