The Mechanical Alignment of Dust (MAD) I: On the spin-up process of fractal grains by a gas-dust drift

Abstract

Context: Aligned dust grains are commonly exploited to probe the magnetic field orientation. However, the exact physical processes that result in a coherent large-scale grain alignment are far from being constrained. Aims: In this work, we aim to investigate the impact of a gas-dust drift leading to a mechanical alignment of dust (MAD) and to dust polarization. Methods: We explore fractal dust aggregates to statistically analyze the average alignment behavior of distinct grain ensembles. The spin-up efficiencies for individual aggregates are determined utilizing MC simulations. These efficiencies are analyzed to identify stable points for the grain alignment in direction of the gas-dust drift and along the magnetic field lines. Finally, the net dust polarization is calculated per grain ensemble. Results: The mechanical spin-up within the CNM is sufficient to drive grains to a stable alignment. A likely mechanical grain alignment is parallel to the drift direction. All grains can align at subsonic conditions. Here, we predict a polarization efficiency in the order of unity for the MAD. A supersonic drift may result in a rapid rotation where dust grains may become rotationally disrupted and the polarization becomes drastically reduced. In the presence of a magnetic field, the drift required for the alignment of elongated grains is roughly one order of magnitude higher compared to the pure MAD. Here, the dust polarization efficiency is 0.6-0.9 indicating that a drift can provide the prerequisites to probe the magnetic field. The alignment is inefficient when the direction of the drift and the field lines are perpendicular. Conclusions: We find that MAD has to be taken into consideration as an alternative driving mechanism where the standard RAT alignment theory fails to account for the full spectrum of available dust polarization observations.

27 pages, 29 figures, 3 tables

References in corpus (31)

• Radiative torques: Analytical Model and Basic Properties
• The evolution of amorphous hydrocarbons in the ISM: dust modelling from a new vantage point
• Radiative torque alignment: Essential Physical Processes
• The Efficiency of Grain Alignment in Dense Interstellar Clouds: A Reassessment of Constraints from Near Infrared Polarization
• Modeling Porous Dust Grains with Ballistic Aggregates I: Geometry and Optical Properties
• Grain Alignment by Radiative Torques in Special Conditions and Implications
• Subsonic Mechanical Alignment of Irregular Grains
• On the radiation driven alignment of dust grains: Detection of the polarization hole in a starless core
• CELES: CUDA-accelerated simulation of electromagnetic scattering by large ensembles of spheres
• Radiative torques alignment in the presence of pinwheel torques
• Alignment of Dust with Magnetic Inclusions: Radiative Torques and Superparamagnetic Barnett and Nuclear Relaxation
• Grain Alignment in Starless Cores
• From parallel to perpendicular -- On the orientation of magnetic fields in molecular clouds
• Dust Polarization Toward Embedded Protostars in Ophiuchus with ALMA. III. Survey Overview
• Observational Constraints on Interstellar Grain Alignment
• Indirect evidence of significant grain growth in young protostellar envelopes from polarized dust emission
• Tensile Strength of Porous Dust Aggregates
• A statistical analysis of dust polarization properties in ALMA observations of Class 0 protostellar cores
• Millimeter-wave polarization due to grain alignment by the gas flow in protoplanetary disks
• Compression Behaviour of Porous Dust Agglomerates
• Modeling Grain Alignment by Radiative Torques and Hydrogen Formation Torques in Reflection Nebula
• Alignment of irregular grains by radiative torques: efficiency study
• A systematic study of radiative torque grain alignment in the diffuse interstellar medium
• Effects of grain alignment with magnetic fields on grain growth and the structure of dust aggregates
• OMC-1 dust polarisation in ALMA Band 7: Diagnosing grain alignment mechanisms in the vicinity of Orion Source I
• Interferometric Mapping of Magnetic fields: NGC2071IR
• The Explosion in Orion-KL as Seen by Mosaicking the Magnetic Field with ALMA
• Magnetic fields in star-forming systems (II): examining dust polarization, the Zeeman effect, and the Faraday rotation measure as magnetic field tracers
• Condensation of cometary silicate dust using an induction thermal plasma system I. Enstatite and CI chondritic composition
• Linear dust polarization during the embedded phase of protostar formation
• The Acoustic Resonant Drag Instability with a Spectrum of Grain Sizes

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