Magnetic fields are generally expected to increase the characteristic mass of stars formed in stellar clusters, because they tend to increase the effective Jeans mass. We test this expectation using adaptive mesh refinement (AMR) magnetohydrodynamic simulations of cluster formation in turbulent magnetized clumps of molecular clouds, treating stars as accreting sink particles. We find that, contrary to the common expectation, a magnetic field of strength in the observed range decreases, rather than increases, the characteristic stellar mass. It (1) reduces the number of intermediate-mass stars that are formed through direct turbulent compression, because sub-regions of the clump with masses comparable to those of stars are typically magnetically subcritical and cannot be compressed directly into collapse, and (2) increases the number of low-mass stars that are produced from the fragmentation of dense filaments. The filaments result from mass accumulation along the field lines. In order to become magnetically supercritical and fragment, the filament must accumulate a large enough column density (proportional to the field strength), which yields a high volume density (and thus a small thermal Jeans mass) that is conducive to forming low-mass stars. We find, in addition, that the characteristic stellar mass is reduced further by outflow feedback. The conclusion is that both magnetic fields and outflow feedback are important in shaping the stellar initial mass function (IMF).
Observations of Protostellar Outflow Feedback in Clustered Star Formation
我们讨论了原恒星外流反馈的作用，在集群恒星形成的观测数据，最近的分子外流调查对附近的集群形成团块。我们发现，对于几乎所有的团块，流出动量注入率是显着大于湍流耗散率。因此，外流反馈很可能维持团簇中的超音速湍流。对于质量较小的团块，如B59、L1551和L1641 N，流出的动能与团块的引力能相当。在这样的集群，外流反馈可能会影响显着的集群动力学。另一方面，对于质量大于约200 M $_\odot$的团块，流出动能明显小于团块的重力能。由于大多数恒星都是在这样的团块中形成的，我们得出结论，外流反馈不能摧毁整个母体团块。外流反馈的这些特征支持恒星形成缓慢的假设。
Unveiling Stellar Feedback and Cloud Structure in the $ρ$ Ophiuchi A Region with ALMA and JWST: Discovery of Substellar Cores, C$^{18}$O Striations, and Protostellar Outflows
