  This letter studies the formation of azimuthal metallicity variations in the
disks of spiral galaxies in the absence of initial radial metallicity
gradients. Using high-resolution $N$-body simulations, we model composite
stellar discs, made of kinematically cold and hot stellar populations, and
study their response to spiral arm perturbations. We find that, as expected,
disk populations with different kinematics respond differently to a spiral
perturbation, with the tendency for dynamically cooler populations to show a
larger fractional contribution to spiral arms than dynamically hotter
populations. By assuming a relation between kinematics and metallicity, namely
the hotter the population, the more metal-poor it is, this differential
response to the spiral arm perturbations naturally leads to azimuthal
variations in the mean metallicity of stars in the simulated disk. Thus,
azimuthal variations in the mean metallicity of stars across a spiral galaxy
are not necessarily a consequence of the reshaping, by radial migration, of an
initial radial metallicity gradient. They indeed arise naturally also in
stellar disks which have initially only a negative vertical metallicity
gradient.
