Remodeling the evolution of grain size distribution in galaxies
  We revisit the evolution model of grain size distribution in a galaxy for the
ultimate purpose of implementing it in hydrodynamical simulations. We simplify
the previous model in such a way that some model-dependent assumptions are
replaced with simpler functional forms. For the first test of the developed
framework, we apply it to a one-zone chemical evolution model of a galaxy,
confirming that our new model satisfactorily reproduces the previous results
and that efficient coagulation of small grains produced by shattering and
accretion is essential in reproducing the so-called MRN grain size
distribution. For the next step, in order to test if our model can be treated
together with the hydrodynamical evolution of the interstellar medium (ISM), we
post-process a hydrodynamical simulation of an isolated disc galaxy using the
new grain evolution model. We sample hydrodynamical particles representing each
of the dense and diffuse ISM phases. By this post-processing, we find that the
processes occurring in the dense gas (grain growth by accretion and
coagulation) are important in reproducing the grain size distribution
consistent with the Milky Way extinction curve. In our model, the grain size
distributions are similar between the dense and diffuse ISM, although we
observe a larger dispersion in the dense ISM. Moreover, we also show that even
if we degrade the grain radius resolution (with 16 grid points), the overall
shape of grain size distribution (and of resulting extinction curve) can be
captured.
