2014MNRAS.444.2085D

The discovery of a hyper metal-poor star with total metallicity of ≤ 10^–5 Z_☉ has motivated new investigations of how such objects can form from primordial gas polluted by a single supernova. In this paper, we present a shock-cloud model which simulates a supernova remnant interacting with a cloud in a metal-free environment at redshift z = 10. Pre-supernova conditions are considered, which include a multiphase neutral medium and Hii region. A small dense clump (n = 100 cm-3), located 40pc from a 40M_☉ metal-free star, embedded in an n = 10 cm-3 ambient cloud. The evolution of the supernova remnant and its subsequent interaction with the dense clump is examined. We include a comprehensive treatment of the non-equilibrium hydrogen and helium chemistry and associated radiative cooling that is occurring at all stages of the shock-cloud model, covering the temperature range 10-10⁹K. Deuterium chemistry and its associated cooling are not included because the UV radiation field produced by the relic Hii region and supernova remnant is expected to suppress deuterium chemistry and cooling. We find a 10³ times density enhancement of the clump (maximum density ~78000 cm-3) within this metal-free model. This is consistent with Galactic shock-cloud models considering solar metallicity gas with equilibrium cooling functions. Despite this strong compression, the cloud does not become gravitationally unstable. We find that the small cloud modelled here is destroyed for shock velocities ≳ 50 km/s, and not significantly affected by shocks with velocity ≲ 30 km/s. Rather specific conditions are required to make such a cloud collapse, and substantial further compression would be required to reduce the local Jeans mass to sub-solar values.