Dissipation of magnetic fields in star-forming clouds with different metallicities

Abstract

We study dissipation process of magnetic fields in the metallicity range $0-1 Z_{\odot}$ for contracting prestellar cloud cores. By solving non-equilibrium chemistry for important charged species including charged grains, we evaluate the drift velocity of the magnetic-field lines with respect to the gas. We find that the magnetic flux dissipates in the density range $10^{12}{\rm cm^{-3}} \lesssim n_{\rm H} \lesssim 10^{17}{\rm cm^{-3}}$ for the solar-metallicity case at the scale of the core, which is assumed to be the Jeans scale. The dissipation density range becomes narrower for lower metallicity. The magnetic field is always frozen to the gas below metallicity $\lesssim 10^{-7}-10^{-6}Z_\odot$, depending on the ionization rate by cosmic rays and/or radioactivity. With the same metallicity, the dissipation density range becomes wider for lower ionization rate. The presence of such a dissipative regime is expected to cause various dynamical phenomena in protostellar evolution such as the suppression of jet/outflow launching and fragmentation of the circumstellar disks depending on the metallicity.