OMC-1 dust polarisation in ALMA Band 7: Diagnosing grain alignment mechanisms in the vicinity of Orion Source I

Abstract

We present ALMA Band 7 polarisation observations of the OMC-1 region of the Orion molecular cloud. We find that the polarisation pattern observed in the region is likely to have been significantly altered by the radiation field of the $>10^4$ L${}_{\odot }$ high-mass protostar Orion Source I. In the protostar's optically thick disc, polarisation is likely to arise from dust self-scattering. In material to the south of Source I - previously identified as a region of 'anomalous' polarisation emission - we observe a polarisation geometry concentric around Source I. We demonstrate that Source I's extreme luminosity may be sufficient to make the radiative precession timescale shorter than the Larmor timescale for moderately large grains ($>0.005-0.1\mu$m), causing them to precess around the radiation anisotropy vector (k-RATs) rather than the magnetic field direction (B-RATs). This requires relatively unobscured emission from Source I, supporting the hypothesis that emission in this region arises from the cavity wall of the Source I outflow. This is one of the first times that evidence for k-RAT alignment has been found outside of a protostellar disc or AGB star envelope. Alternatively, the grains may remain aligned by B-RATs and trace gas infall onto the Main Ridge. Elsewhere, we largely find the magnetic field geometry to be radial around the BN/KL explosion centre, consistent with previous observations. However, in the Main Ridge, the magnetic field geometry appears to remain consistent with the larger-scale magnetic field, perhaps indicative of the ability of the dense Ridge to resist disruption by the BN/KL explosion.

20 pages, 20 figures, 3 tables, accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS)

References in corpus (27)

• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• Coagulation, fragmentation and radial motion of solid particles in protoplanetary disks
• Radiative torques: Analytical Model and Basic Properties
• The Gould's Belt Distances Survey (GOBELINS) II. Distances and structure towards the Orion Molecular Clouds
• Disk-Driven Rotating Bipolar Outflow in Orion Source I
• The JCMT BISTRO Survey: The magnetic field strength in the Orion A filament
• Interferometric observations of magnetic fields in forming stars
• Subsonic Mechanical Alignment of Irregular Grains
• Magnetized filamentary gas flows feeding the young embedded cluster in Serpens South
• Submillimeter and Far-Infrared Polarimetric Observations of Magnetic Fields in Star-Forming Regions
• Imaging the Ionized Disk of the High-Mass Protostar Orion-I
• Overview of the Orion Complex
• ALMA Observations of Orion Source I at 350 and 660 GHz
• Millimeter-wave polarization due to grain alignment by the gas flow in protoplanetary disks
• The Orion Protostellar Explosion and Runaway Stars Revisited: Stellar Masses, Disk Retention, and an Outflow from BN
• The Proper Motions of the Double Radio Source n in the Orion BN/KL Region
• New Evidence for the Dynamical Decay of a Multiple System in the Orion Kleinmann-Low Nebula
• ALMA Imaging of Millimeter/Submillimeter Continuum Emission in Orion KL
• Self-scattering of non-spherical dust grains
• Hubble Space Telescope NICMOS Polarization Measurements of OMC-1
• ALMA Images of the Orion Hot Core at 349 GHz
• NICMOS Observations of Shocked H_2 in Orion
• The Explosion in Orion-KL as Seen by Mosaicking the Magnetic Field with ALMA
• Observations of Orion Source I Disk and Outflow Interface
• Magnetic Field Structure of Orion Source I
• Search for Alignment of Disk Orientations in Nearby Star-Forming Regions: Lupus, Taurus, Upper Scorpius, $\rho$ Ophiuchi, and Orion
• Extremely high excitation SiO lines in disk-outflow system in Orion Source I

Cited by in corpus (15)

• B-fields in Star-Forming Region Observations (BISTRO): Magnetic Fields in the Filamentary Structures of Serpens Main
• SOFIA observations of 30 Doradus: I -- Far-Infrared dust polarization and implications for grain alignment and disruption by radiative torques
• The Explosion in Orion-KL as Seen by Mosaicking the Magnetic Field with ALMA
• The Mechanical Alignment of Dust (MAD) I: On the spin-up process of fractal grains by a gas-dust drift
• Atacama Large Aperture Submillimeter Telescope (AtLAST) Science: Our Galaxy
• Three-dimensional magnetic fields of molecular clouds
• Magnetic Field of Molecular Gas Measured with the Velocity Gradient Technique I. Orion A
• Is the mm/submm dust polarization a robust tracer of the magnetic field topology in protostellar envelopes? A model exploration
• Magnetic fields and outflows in the large Bok globule CB 54
• The JCMT BISTRO-2 Survey: The Magnetic Field in the Center of the Rosette Molecular Cloud
• Physical conditions for dust grain alignment in Class 0 protostellar cores II. The role of the radiation field in models aligning/disrupting dust grains
• Ultraviolet Spectropolarimetry with Polstar: Interstellar Medium Science
• Synthetic Modelling of Polarized Dust Emission in Intermediate-Mass YSOs: I: Constraining the Role of Iron Inclusions and Inelastic Relaxation on Grain Alignment with ALMA Polarization
• The generation and transformation of polarisation signals in molecular lines through collective anisotropic resonant scattering
• Synthetic Polarization Maps of an Outflow Zone from Magnetohydrodynamic Simulations