Evolution of Magnetic Fields in Collapsing Star-forming Clouds under
  Different Environments
  In nearby star-forming clouds, amplification and dissipation of the magnetic
field are known to play crucial roles in the star-formation process. The
star-forming environment varies from place to place and era to era in galaxies.
In the present study, amplification and dissipation of magnetic fields in
star-forming clouds are investigated under different environments using
magnetohydrodynamics (MHD) simulations. We consider various star-forming
environments in combination with the metallicity and the ionization strength,
and prepare prestellar clouds having two different mass-to-flux ratios. We
calculate the cloud collapse until protostar formation using ideal and
non-ideal (inclusion and exclusion of Ohmic dissipation and ambipolar
diffusion) MHD calculations to investigate the evolution of the magnetic field.
We perform 288 runs in total and show the diversity of the density range within
which the magnetic field effectively dissipates, depending on the environment.
In addition, the dominant dissipation process (Ohmic dissipation or ambipolar
diffusion) is shown to strongly depend on the star-forming environment.
Especially, for the primordial case, magnetic field rarely dissipates without
ionization source, while it efficiently dissipates when very weak ionization
sources exist in the surrounding environment. The results of the present study
help to clarify star formation in various environments.
