Conditions for circumstellar disc formation: effects of initial cloud configuration and sink treatment

The formation of a circumstellar disc in collapsing cloud cores is investigated with three-dimensional magnetohydrodynamic simulations. We prepare four types of initial cloud having different density profiles and calculate their evolution with or without a sink. To investigate the effect of magnetic dissipation on disc formation, Ohmic dissipation is considered in some models. Calculations show that disc formation is very sensitive to both the initial cloud configuration and the sink treatment. The disc size considerably differs in clouds with different density profiles even when the initial clouds have almost the same mass-to-flux ratio. Only a very small disc (similar to 10 au in size) appears in clouds with a uniform density profile, whereas a large disc (similar to 100 au in size) forms in clouds with a Bonnor-Ebert density profile. In addition, a large sink accretion radius numerically impedes disc formation during the main accretion phase and tends to foster the misleading notion that disc formation is completely suppressed by magnetic braking. The protostellar outflow is also greatly affected by the sink properties. A sink accretion radius of less than or similar to 1 au and sink threshold density of greater than or similar to 10(13) cm(-3) are necessary for investigating disc formation during the main accretion phase.