Non-ideal MHD and protostellar feedback effects on disk formation and evolution in numerical simulations of star cluster formation

Abstract

While recent surveys have resolved hundreds of nearby protostellar disks, numerical simulations assuming ideal magnetohydrodynamics (MHD) have historically struggled to achieve disk formation due to efficient angular momentum removal by magnetic torques. Non-ideal MHD effects, relevant at the low ionization fractions typical of molecular clouds, have been shown to reduce the effectiveness of magnetic braking and promote disk formation. In this work, we present the results from a suite of calculations following the gravitational collapse of 50 M⊙ turbulent molecular cloud cores down to the formation and evolution of stellar systems and protostellar disks. We use the radiation-MHD code gizmo including non-ideal MHD (Ohmic resistivity, ambipolar diffusion, and the Hall effect) and the starforge numerical framework for modeling star formation and stellar feedback. We compare the effects of assuming ideal vs. non-ideal MHD and including sub-grid protostellar jet feedback on disk formation and evolution. Disks form in all of our models but are least massive in the model with ideal MHD and sub-grid jet feedback. Apart from the ideal MHD+jets model, we do not observe any significant differences in disk properties between the ideal and non-ideal MHD models; however, ideal MHD disks are embedded in smaller rotating envelopes. Disk sizes are in general agreement with those of observed disks. Jet feedback increases core fragmentation and reduces final stellar masses. Our results suggest that magnetic braking does not efficiently suppress disk formation, regardless of whether ideal or non-ideal MHD is assumed, under the dynamical conditions in which multiple stellar systems form.