The Effects of Magnetic Fields and Protostellar Feedback on Low-mass Cluster Formation

摘要

We present a large suite of simulations of the formation of low-mass starclusters. Our simulations include an extensive set of physical processes --magnetohydrodynamics, radiative transfer, and protostellar outflows -- and spana wide range of virial parameters and magnetic field strengths. Comparing theoutcomes of our simulations to observations, we find that simulations remainingclose to virial balance throughout their history produce star formationefficiencies and initial mass function (IMF) peaks that are stable in time andin reasonable agreement with observations. Our results indicate thatsmall-scale dissipation effects near the protostellar surface provide afeedback loop for stabilizing the star formation efficiency. This is trueregardless of whether the balance is maintained by input of energy from largescale forcing or by strong magnetic fields that inhibit collapse. In contrast,simulations that leave virial balance and undergo runaway collapse form starstoo efficiently and produce an IMF that becomes increasingly top-heavy withtime. In all cases we find that the competition between magnetic flux advectiontoward the protostar and outward advection due to magnetic interchangeinstabilities, and the competition between turbulent amplification andreconnection close to newly-formed protostars renders the local magnetic fieldstructure insensitive to the strength of the large-scale field, ensuring thatradiation is always more important than magnetic support in setting thefragmentation scale and thus the IMF peak mass. The statistics of multiplestellar systems are similarly insensitive to variations in the initialconditions and generally agree with observations within the range ofstatistical uncertainty.