Dust Destruction in the High-Velocity Shocks Driven by Supernovae in the   Early Universe
  We investigate the destruction of dust grains by sputtering in the high-velocity interstellar shocks driven by supernovae (SNe) in the early universe to reveal the dependence of the time-scale of dust destruction on the gas density $n_{{\rm H}, 0}$ in the interstellar medium (ISM) as well as on the progenitor mass $M_{\rm pr}$ and explosion energy $E_{\rm 51}$ of SN. The sputtering yields for the combinations of dust and ion species of interest to us are evaluated by applying the so-called universal relation with a slight modification. The dynamics of dust grains and their destruction by sputtering in shock are calculated by taking into account the size distribution of each dust species, together with the time evolution of temperature and density of gas in spherically symmetric shocks. The results of calculations show that the efficiency of dust destruction depends not only on the sputtering yield but also on the initial size distribution of each grain species. The efficiency of dust destruction increases with increasing $E_{\rm 51}$ and/or increasing $n_{{\rm H}, 0}$, but is almost independent of $M_{\rm pr}$ as long as $E_{\rm 51}$ is the same. The mass of gas swept up by shock is the increasing function of $E_{\rm 51}$ and the decreasing function of $n_{{\rm H}, 0}$. Combining these results, we present the approximation formula for the time-scale of destruction for each grain species in the early universe as a function of $E_{\rm 51}$ and $n_{{\rm H}, 0}$. This formula is applicable for investigating the evolution of dust grains at the early epoch of the universe with the metallicity of $Z \la 10^{-3}$ $Z_\odot$. The effects of the cooling processes of gas on the destruction of dust are briefly discussed. 
Takaya Nozawa, Takashi Kozasa, Asao Habe (Hokkaido University)