2018MNRAS.480.1043N

Shocks may have been prevalent in the early Universe, associated with virialization and supernova explosions, etc. Here, we study thermal evolution and fragmentation of shock-compressed clouds, by using a one-zone model with detailed thermal and chemical processes. We explore a large range of initial density (1-10⁵ cm^–3), metallicity (0-10^–2 Z_☉), UV strength (0-500 times Galactic value), and cosmic microwave background temperature (10 and 30 K). Shock-compressed clouds contract isobarically via atomic and molecular line cooling, until self-gravitating clumps are formed by fragmentation. If the metals are only in the gas-phase, the clump mass is higher than ∼3 M_☉ in any conditions we studied. Although in some cases with a metallicity higher than ∼10^–3 Z_☉, re-fragmentation of a clump is caused by metal-line cooling, this fragment mass is higher than ∼30 M_☉. On the other hand, if about half the mass of metals is condensed in dust grains, as in the Galactic interstellar medium, dust cooling triggers re-fragmentation of a clump into subsolar mass pieces, for metallicities higher than ∼10^–5 Z_☉. Therefore, the presence of dust is essential in low-mass (<= M_☉) star formation from a shock-compressed cloud.