The effects of accretion luminosity upon fragmentation in the early universe

We introduce a prescription for the luminosity from accreting protostars into smoothed particle hydrodynamics simulation and apply the method to simulations of five primordial minihaloes generated from cosmological initial conditions. We find that accretion luminosity delays fragmentation with in the haloes but does not prevent it. In haloes that slowly form a low number of protostars, the accretion luminosity can reduce the number of fragments that are formed before the protostars start ionizing their surroundings. However, haloes that rapidly form many protostars become dominated by dynamical processes, and the effect of accretion luminosity becomes negligible. Generally, the fragmentation found in the haloes is highly dependent on the initial conditions. Accretion luminosity does not substantially affect the accretion rates experienced by the protostars and is far less important than dynamical interactions, which can lead to ejections that effectively terminate the accretion. We find that the accretion rates on to the inner regions of the discs (20 au) around the protostars are highly variable, in contrast to the constant or smoothly decreasing accretion rates currently used in models of the pre-main-sequence evolution of Population III stars.