Multi-scale Dust Polarization and Spiral-like Stokes-I Residual in the Class I Protostellar System TMC-1A

Abstract

We have observed the Class I protostar TMC-1A in the Taurus molecular cloud using the Submillimeter Array (SMA) and the Atacama Large Millimeter/submillimeter Array (ALMA) in the linearly polarized 1.3 mm continuum emission at angular resolutions of ~3" and ~0.3", respectively. The ALMA observations also include CO, 13CO, and C18O J=2-1 spectral lines. The SMA observations trace magnetic fields on the 1000-au scale, the directions of which are neither parallel nor perpendicular to the outflow direction. Applying the Davis-Chandrasekhar-Fermi method to the SMA polarization angle dispersion, we estimate a field strength in the TMC-1A envelope of 1-5 mG. It is consistent with the field strength needed to reduce the radial infall velocity to the observed value, which is substantially less than the local} free-fall velocity. The ALMA polarization observations consist of two distinct components -- a central component and a north/south component. The central component shows polarization directions in the disk minor axis to be azimuthal, suggesting dust self-scattering in the TMC-1A disk. The north/south component is located along the outflow axis and the polarization directions are aligned with the outflow direction. We discuss possible origins of this polarization structure, including grain alignment by a toroidal magnetic field and mechanical alignment by the gaseous outflow. In addition, we discover a spiral-like residual in the total intensity (Stokes I) for the first time. The C18O emission suggests that material in the spiral-like structure is infalling at a speed that is 20% of the local Keplerian speed.

22 pages, 14 figures, accepted for publication in The Astrophysical Journal

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Cited by in corpus (4)

• On Internal and External Alignment of Dust Grains in Protostellar Environments
• (Sub)millimeter Dust Polarization of Protoplanetary Disks from Scattering by Large Millimeter-Sized Irregular Grains
• Cloudlet Capture Model for Asymmetric Molecular Emission Lines Observed in TMC-1A with ALMA
• Is the mm/submm dust polarization a robust tracer of the magnetic field topology in protostellar envelopes? A model exploration