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Star Formation Triggered by Supernova Explosions in Young Galaxies

We study the evolution of supernova remnants in a low-metallicity medium $Z/Z_{\odot} = 10^{-4}$ -- $10^{-2}$ in the early universe, using one-dimensional hydrodynamics with non-equilibrium chemistry. Once a post-shock layer is able to cool radiatively, a dense shell forms behind the shock. If this shell becomes gravitationally unstable and fragments into pieces, next-generation stars are expected to form from these fragments. To explore the possibility of this triggered star formation, we apply a linear perturbation analysis of an expanding shell to our results and constrain the parameter range of ambient density, explosion energy, and metallicity where fragmentation of the shell occurs. For the explosion energy of $10^{51}{\rm ergs} (10^{52}{\rm ergs})$, the shell fragmentation occurs for ambient densities higher than $\gtrsim 10^{2} {\rm cm^{-3}}$ (10 ${\rm cm^{-3}}$, respectively). This condition depends little on the metallicity in the ranges we examined. We find that the mode of star formation triggered occurs only in massive ($\gtrsim 10^{8}M_{\odot}$) haloes.