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

TL;DR

This study investigates how magnetic fields dissipate in star-forming clouds across different metallicities, revealing that dissipation occurs over specific density ranges and is influenced by metallicity and ionization rates, affecting star formation processes.

Contribution

It provides the first detailed analysis of magnetic field dissipation across a range of metallicities using non-equilibrium chemistry, highlighting the conditions under which magnetic flux is frozen or dissipated.

Findings

Magnetic flux dissipates between densities of 10^{12} and 10^{17} cm^{-3} at solar metallicity.

Lower metallicity narrows the dissipation density range, with magnetic fields remaining frozen below 10^{-7}-10^{-6} Z_sun.

Dissipation regimes influence protostellar phenomena like jet launching and disk fragmentation.

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.