2021MNRAS.508.4175C

We study star cluster formation in a low-metallicity environment using three-dimensional hydrodynamic simulations. Starting from a turbulent cloud core, we follow the formation and growth of protostellar systems with different metallicities ranging from 10^–6 to 0.1 Z_☉. The cooling induced by dust grains promotes fragmentation at small scales and the formation of low-mass stars with M_* ∼ 0.01-0.1 M_☉. While the number of low-mass stars increases with metallicity, when Z/Z_☉ >= 10^–5, the stellar mass distribution is still top-heavy for Z/Z_☉ <= 10^–2 compared to the Chabrier initial mass function (IMF). In these cases, star formation begins after the turbulent motion decays and a single massive cloud core monolithically collapses to form a central massive stellar system. The circumstellar disc preferentially feeds the mass to the central massive stars, making the mass distribution top-heavy. When Z/Z_☉ = 0.1, collisions of the turbulent flows promote the onset of the star formation and a highly filamentary structure develops owing to efficient fine-structure line cooling. In this case, the mass supply to the massive stars is limited by the local gas reservoir and the mass is shared among the stars, leading to a Chabrier-like IMF. We conclude that cooling at the scales of the turbulent motion promotes the development of the filamentary structure and works as an important factor leading to the present-day IMF.