2D chemical evolution model: the impact of galactic disc asymmetries on
  azimuthal chemical abundance variations
  Galactic disc chemical evolution models generally ignore azimuthal surface
density variation that can introduce chemical abundance azimuthal gradients.
Recent observations, however, have revealed chemical abundance changes with
azimuth in the gas and stellar components of both the Milky Way and external
galaxies. To quantify the effects of spiral arm density fluctuations on the
azimuthal variations of the oxygen and iron abundances in disc galaxies. We
develop a new 2D galactic disc chemical evolution model, capable of following
not just radial but also azimuthal inhomogeneities. The density fluctuations
resulting from a Milky Way-like N-body disc formation simulation produce
azimuthal variations in the oxygen abundance gradients of the order of 0.1 dex.
Moreover, in agreement with the most recent observations in external galaxies,
the azimuthal variations are more evident in the outer galactic regions. Using
a simple analytical model, we show that the largest fluctuations with azimuth
result near the spiral structure corotation resonance, where the relative speed
between spiral and gaseous disc is the slowest. In conclusion we provided a new
2D chemical evolution model capable of following azimuthal density variations.
Density fluctuations extracted from a Milky Way-like dynamical model lead to a
scatter in the azimuthal variations of the oxygen abundance gradient in
agreement with observations in external galaxies. We interpret the presence of
azimuthal scatter at all radii by the presence of multiple spiral modes moving
at different pattern speeds, as found in both observations and numerical
simulations.
