On Internal and External Alignment of Dust Grains in Protostellar Environments

Abstract

We study the physical processes inducing the alignment of the grain axis of maximum inertia moment with the angular momentum ($\mathbf{J}$, i.e., internal alignment) and of $\mathbf{J}$ with the magnetic field (i.e., external alignment) of very large grains (VLGs, of radius $a>10\mu$m) using the grain alignment framework based on radiative torques (RATs) and mechanical torques (METs). We derive analytical formulae for critical sizes of grain alignment, assuming that grains are aligned at both low$-J$ and high$-J$ attractors by RATs (METs). For protostellar cores, we find that super-Barnett relaxation can induce efficient internal alignment for VLGs with large iron inclusions aligned at high$-J$ attractors by RATs (METs). In contrast, inelastic relaxation can be efficient for VLGs made of any composition. For external alignment, we find that VLGs with iron inclusions aligned at high$-J$ attractors can have magnetic alignment by RATs ($B-$RAT) or METs ($B-$ MET), enabling dust polarization as a reliable tracer of magnetic fields in such dense regions. Still, grains at low$-J$ attractors or grains without iron inclusions have alignment along the radiation direction ($k-$RAT) or gas flow ($v-$MET). For protostellar disks, we find that super-Barnett relaxation can be efficient for grains with large iron inclusions in the outer disk thanks to spinup by METs, but inelastic relaxation is inefficient. VLGs aligned at low-J attractors can have $k-$RAT ($v-$MET) alignment, but grains aligned at high$-J$ attractors have likely $B-$RAT ($B-$MET) alignment. Grain alignment by METs appears to be more important than RATs in protostellar disks.

43 pages, 17 figures, Table of notations is added. Version accepted

References in corpus (27)

• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• Radiative torques: Analytical Model and Basic Properties
• Planck intermediate results. XIX. An overview of the polarized thermal emission from Galactic dust
• Tracing Magnetic Fields with Aligned Grains
• Gaps, Rings, and Non-Axisymmetric Structures in Protoplanetary Disks - From Simulations to ALMA Observations
• Magnetic Fields and Massive Star Formation
• Radiative torque alignment: Essential Physical Processes
• The evidence of radio polarization induced by the radiative grain alignment and self-scattering of dust grains in a protoplanetary disk
• Grain growth in the envelopes and disks of Class I protostars
• ALMA Reveals Transition of Polarization Pattern with Wavelength in HL Tau's Disk
• Grain Alignment by Radiative Torques in Special Conditions and Implications
• Submillimeter polarization observation of the protoplanetary disk around HD 142527
• Interferometric observations of magnetic fields in forming stars
• Subsonic Mechanical Alignment of Irregular Grains
• Grain Alignment and Polarized Emission from Magnetized T Tauri Disks
• Low dust emissivities and radial variations in the envelopes of Class 0 protostars: a signature of early grain growth?
• Submillimeter and Far-Infrared Polarimetric Observations of Magnetic Fields in Star-Forming Regions
• Radiative torques alignment in the presence of pinwheel torques
• Alignment of Dust with Magnetic Inclusions: Radiative Torques and Superparamagnetic Barnett and Nuclear Relaxation
• Millimeter-wave polarization due to grain alignment by the gas flow in protoplanetary disks
• Solving grain size inconsistency between ALMA polarization and VLA continuum in the Ophiuchus IRS 48 protoplanetary disk
• Polarized emission by aligned grains in the Mie regime : application to protoplanetary disks observed by ALMA
• Extragalactic magnetism with SOFIA (SALSA Legacy Program) -- III: First data release and on-the-fly polarization mapping characterization
• Modeling of the ALMA HL Tau Polarization by Mixture of Grain Alignment and Self-scattering
• Accretion Burst Echoes as Probes of Protostellar Environments and Episodic Mass Assembly
• Thermal Emission and Scattering by Aligned Grains: Plane-Parallel Model and Application to Multiwavelength Polarization of the HL Tau Disk
• Multi-scale Dust Polarization and Spiral-like Stokes-I Residual in the Class I Protostellar System TMC-1A

Cited by in corpus (15)

• SOFIA observations of 30 Doradus: II -- Magnetic fields and large scale gas kinematics
• Physical Modeling of Dust Polarization from Magnetically Enhanced Radiative Torque (MRAT) Alignment in Protostellar Cores with POLARIS
• B-fields And dust in interstelLar fiLAments using Dust POLarization (BALLAD-POL): I. The massive filament G11.11-0.12 observed by SOFIA/HAWC+
• Observationally derived magnetic field strength and 3D components in the HD 142527 disk
• Physical conditions for dust grain alignment in Class 0 protostellar cores I. Observations of dust polarization and molecular irradiation tracers
• Three-dimensional magnetic field imaging of protoplanetary disks using Zeeman broadening and linear polarization observations
• Evidence of Grain Alignment by Magnetically Enhanced Radiative Torques from Multiwavelength Dust Polarization Modeling of HL Tau
• Physical conditions for dust grain alignment in Class 0 protostellar cores II. The role of the radiation field in models aligning/disrupting dust grains
• Mapping and characterizing magnetic fields in the Rho Ophiuchus-A molecular cloud with SOFIA/HAWC$+$
• 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 origin of dust polarization in the Orion Bar
• Alignment and Rotational Disruption of Dust Grains in the Galactic Centre Revealed by Polarized Dust Emission
• Grain alignment and dust evolution physics with polarisation (GRADE-POL). I. Dust polarisation modelling for isolated starless cores
• Silicate Sundogs: Probing the Effects of Grain Directionality in Exoplanet Observations
• Polarized microwave emission from space particles in the upper atmosphere of the Earth