Chemical evolution of elliptical galaxies with a variable IMF -- A
  publicly available code
  Growing evidence in recent years suggests a systematic variation of the
stellar initial mass function (IMF), being top-heavy for starburst galaxies and
possibly bottom-heavy for massive ellipticals. Galaxy chemical evolution
simulations adopting an invariant canonical IMF face difficulty in
simultaneously reproducing the metallicity and $\alpha$-enhancement of the
massive elliptical galaxies. Applying a variable IMF that changes with time is
a promising solution, however, it is non-trivial to couple a variable IMF
theory with the existing galaxy evolution codes. Here we present the first open
source simulation code which recalculates the galaxy-wide IMF at each time step
according to the Integrated-Galactic-IMF (IGIMF) theory where the galaxy-wide
IMF depends on the galactic star formation rate and metallicity. The resulting
galaxy-wide IMF and metal abundance evolve with time. With this pilot work, we
explore the effect of the IGIMF theory on galaxy chemical evolution in
comparison with an invariant IMF.
