Radiation Magnetohydrodynamic Simulations of Protostellar Collapse: Low-Metallicity Environments

Abstract: Among many physical processes involved in star formation, radiation transfer is one of the key processes since it dominantly controls the thermodynamics. Because metallicities control opacities, they are one of the important environmental parameters which affect star formation processes. In this work, I investigate protostellar collapse in solar-metallicity and low-metallicity ($Z = 0.1 Z_\odot$) environments using 3D radiation hydrodynamic and magnetohydrodynamic simulations. Because radiation cooling is more effective in the low-metallicity environments, first cores are colder and have lower entropies. As a result, first cores are smaller, less massive and have shorter lifetimes in the low-metallicity clouds. Therefore, first cores would be less likely to be found in low-metallicity star forming clouds. This also implies that first cores tend to be more gravitationally unstable and susceptible to fragmentation. The evolution and structure of protostellar cores formed after the second collapse weakly depend on metallicities in the spherical and magnetized models despite the large difference in the metallicities. Because this is due to the change of the heat capacity by dissociation and ionization of hydrogen, it is a general consequence of the second collapse as long as the effects of radiation cooling are not very large during the second collapse. On the other hand, the effects of different metallicities are more significant in the rotating models without magnetic fields, because they evolve slower than other models and therefore more affected by radiation cooling.