Highly Ordered and Pinched Magnetic Fields in the Class 0 Proto-Binary System L1448 IRS 2

TL;DR

This study uses ALMA polarimetric observations to reveal a complex magnetic field structure in the Class 0 proto-binary L1448 IRS 2, suggesting mechanisms that may prevent magnetic braking and influence disk formation.

Contribution

First high-resolution polarimetric imaging of L1448 IRS 2 revealing detailed magnetic field morphology and its implications for disk formation and magnetic braking.

Findings

Hourglass magnetic field morphology observed

Possible circumstellar disk indicated by toroidal field

Magnetic field strength may hinder disk formation

Abstract

We have carried out polarimetric observations with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the Class 0 protostellar system L1448 IRS 2, which is a proto-binary embedded within a flattened, rotating structure, and for which a hint of a central disk has been suggested, but whose magnetic fields are aligned with the bipolar outflow on the cloud core scale. Our high sensitivity and high resolution ($\sim 100$ au) observations show a clear hourglass magnetic field morphology centered on the protostellar system, but the central pattern is consistent with a toroidal field indicative of a circumstellar disk, although other interpretations are also possible, including field lines dragged by an equatorial accretion flow into a configuration parallel to the midplane. If a relatively large disk does exist, it would suggest that the magnetic braking catastrophe is averted in this system, not through a large misalignment between the magnetic and rotation axes, but rather through some other mechanisms, such as non-ideal magneto-hydrodynamic effects and/or turbulence. We have also found a relationship of decreasing polarization fractions with intensities and the various slopes of this relationship can be understood as multiple polarization mechanisms and/or depolarization from a changing field morphology. In addition, we found a prominent clumpy depolarization strip crossing the center perpendicular to the bipolar outflow. Moreover, a rough estimate of the magnetic field strength indicates that the field is strong enough to hinder formation of a rotationally supported disk, which is inconsistent with the feature of a central toroidal field.