The Magnetic Field in Taurus Probed by Infrared Polarization

TL;DR

This study maps the magnetic field in Taurus using infrared polarization, revealing magnetic support in dense regions and a possible influence from a nearby supernova remnant on the magnetic field structure.

Contribution

It provides detailed magnetic field measurements in Taurus, tests grain alignment models, and suggests a supernova remnant impact on magnetic field morphology.

Findings

Magnetic field strength ranges from 5-82 microgauss.

Magnetic support is sub-unity in mass-to-flux ratio.

Magnetic field orientation changes near the B213 filament, indicating interaction with a supernova remnant.

Abstract

We present maps of the plane-of-sky magnetic field within two regions of the Taurus molecular cloud: one in the dense core L1495/B213 filament, the other in a diffuse region to the west. The field is measured from the polarization of background starlight seen through the cloud. In total, we measured 287 high-quality near-infrared polarization vectors in these regions. In L1495/B213, the percent polarization increases with column density up to Av ~ 9 mag, the limits of our data. The Radiative Torques model for grain alignment can explain this behavior, but models that invoke turbulence are inconsistent with the data. We also combine our data with published optical and near-infrared polarization measurements in Taurus. Using this large sample, we estimate the strength of the plane-of-sky component of the magnetic field in nine subregions. This estimation is done with two different techniques that use the observed dispersion in polarization angles. Our values range from 5-82 microgauss and tend to be higher in denser regions. In all subregions, the critical index of the mass-to-magnetic flux ratio is sub-unity, implying that Taurus is magnetically supported on large scales (~2 pc). Within the region observed, the B213 filament makes a sharp turn to the north and the direction of the magnetic field also takes a sharp turn, switching from being perpendicular to the filament to becoming parallel. This behavior can be understood if we are observing the rim of a bubble. We argue that it has resulted from a supernova remnant associated with a recently discovered nearby gamma-ray pulsar.