Outflows, cores, and magnetic field orientations in W43-MM1 as seen by ALMA

Abstract

Aims. It has been proposed that the magnetic field, which is pervasive in the interstellar medium, plays an important role in the process of massive star formation. To better understand the impact of the magnetic field at the pre- and protostellar stages, high-angular resolution observations of polarized dust emission toward a large sample of massive dense cores are needed. We aim to reveal any correlation between the magnetic field orientation and the orientation of the cores and outflows in a sample of protostellar dense cores in the W43-MM1 high-mass star-forming region.

Methods. We used the Atacama Large Millimeter Array in Band 6 (1.3 mm) in full polarization mode to map the polarized emission from dust grains at a physical scale of similar to 2700 au. We used these data to measure the orientation of the magnetic field at the core scale. Then, we examined the relative orientations of the core-scale magnetic field, of the protostellar outflows, and of the major axis of the dense cores determined from a 2D Gaussian fit in the continuum emission.

Results. We find that the orientation of the dense cores is not random with respect to the magnetic field. Instead, the dense cores are compatible with being oriented 20-50 degrees with respect to the magnetic field. As for the outflows, they could be oriented 50-70 degrees with respect to the magnetic field, or randomly oriented with respect to the magnetic field, which is similar to current results in low-mass star-forming regions.

Conclusions. The observed alignment of the position angle of the cores with respect to the magnetic field lines shows that the magnetic field is well coupled with the dense material; however, the 20-50 degrees preferential orientation contradicts the predictions of the magnetically-controlled core-collapse models. The potential correlation of the outflow directions with respect to the magnetic field suggests that, in some cases, the magnetic field is strong enough to control the angular momentum distribution from the core scale down to the inner part of the circumstellar disks where outflows are triggered.