  We investigate the evolution of polycyclic aromatic hydrocarbon (PAH)
abundance in a galaxy, which is a crucial step to understand the evolution of
bright emission features in the mid-infrared range. We calculate the evolution
of dust grain size distribution in a manner consistent with the physical
conditions of the interstellar medium by post-processing our previous
hydrodynamical simulation of an isolated disc galaxy. We also differentiate
between aromatic and non-aromatic grains for carbonaceous dust species and
explicitly considered the aromatization process. As a consequence, our model
explains the metallicity dependence of PAH abundances in nearby galaxies well.
The PAH abundance increase is driven particularly by the interplay between
shattering and accretion (dust growth). The fast aromatization guarantees that
the small carbonaceous grains trace PAHs very well. Since shattering and
accretion are sensitive to the dust abundance, we predict that the PAH-to-dust
abundance ratio increases as the metallicity increases. This is consistent with
the observation data of nearby galaxies.
