Beginning with cosmological initial conditions at z=100, we simulate the effects of magnetic fields on the formation of Population III stars and compare our results with the predictions of Paper I. We use Gadget-2 to follow the evolution of the system while the field is weak. We introduce a new method for treating kinematic fields by tracking the evolution of the deformation tensor. The growth rate in this stage of the simulation is lower than expected for diffuse astrophysical plasmas, which have a very low resistivity (high magnetic Prandtl number); we attribute this to the large numerical resistivity in simulations, corresponding to a magnetic Prandtl number of order unity. When the magnetic field begins to be dynamically significant in the core of the minihalo at z=27, we map it onto a uniform grid and follow the evolution in an adaptive mesh refinement, MHD simulation in Orion2. The nonlinear evolution of the field in the Orion2 simulation violates flux-freezing and is consistent with the theory proposed by Xu & Lazarian. The fields approach equipartition with kinetic energy at densities ~ 10^10 - 10^12 cm^-3. When the same calculation is carried out in Orion2 with no magnetic fields, several protostars form, ranging in mass from ~ 1 to 30 M_sol with magnetic fields, only a single ~ 30 M_sol protostar forms by the end of the simulation. Magnetic fields thus suppress the formation of low-mass Pop III stars, yielding a top-heavy Pop III IMF and contributing to the absence of observed Pop III stars.
Calibration of star formation rate tracers for short- and long-lived star formation episodes
为了获得宇宙中恒星形成的历史，需要一套不同波长的校准恒星形成率示踪剂。校准必须始终考虑到灭绝，恒星形成制度（短或长寿命）和演化状态的影响，以避免在不同的红移范围内的偏差。我们使用进化的合成模型优化激烈的恒星形成的情节，以计算一致的校准最常见的恒星形成率示踪剂在不同的能量范围内，从X射线到射电光度。近瞬时和连续的恒星形成制度，和星际灭绝的影响，以及金属丰度的校准的不同估计的效果。一致的校准一套完整的恒星形成率示踪剂，计算最常见的恒星形成区域的条件：演化状态，恒星形成制度，星际消光和初始质量函数。我们讨论了在不同的恒星形成的情况下，不同的示踪剂的有效性，并比较我们的预测与以前的校准一般使用。近瞬时和连续的恒星形成制度必须加以区分。虽然恒星形成强度（\msun）应该用于前者，但更常见的恒星形成率（\msun yr $^{-1}$）仅适用于在长时间内以恒定速率形成恒星的事件。此外，即使对于后者，也应该考虑到进化状态，因为大多数SFR示踪剂只有在1亿年的进化之后才稳定下来。
