The Role of Dust in the Early Universe I : Protogalaxy Evolution
  We develop one-zone galaxy formation models in the early Universe, taking
into account dust formation and evolution by supernova (SN) explosions.
Especially we focus on the time evolution of dust size distribution, because
${\rm H}_{2}$ formation on the dust surface plays a critical role in the star
formation process in the early Universe. In the model we assume that star
formation rate (SFR) is proportional to the total amount of ${\rm H}_{2}$. We
consistently treat (i) the formation and size evolution of dust, (ii) the
chemical reaction networks including ${\rm H}_{2}$ formation both on the
surface of dust and in gas phase, and (iii) the SFR in the model. First, we
find that, because of dust destruction due to both reverse and forward shocks
driven by SNe, H$_{2}$ formation is more suppressed than that without dust
destruction. At the galaxy age of $sim0.8 {\rm Gyr}$, for galaxy models with
virial mass $M_{\rm vir}=10^{9} M_{\odot}$ and formation redshift $z_{\rm
vir}=10$, the molecular fraction is 2.5 orders of magnitude less in the model
with dust destruction by both shocks than that in the model without dust
destruction. Second, we show that the H$_{2}$ formation rate strongly depends
on the ISM density around SN progenitors. The SFR in higher ISM density is
lower, since dust destruction by reverse shocks is more effective in higher ISM
density. We conclude that not only the amount but also the size distribution of
dust being related with the star formation activity strongly affects the
evolution of galaxies in the early Universe.
