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Effects of Grain Magnetic Properties and Grain Growth on Synthetic Dust Polarization of MHD Simulations in Protostellar Environments
Astrophysics of Galaxies · Submitted 31 Jul 2023
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim Finally, we found the increase of polarization angle dispersion function $S$ with iron inclusions and grain growth, implying the dependence of B-field strength measured using the DCF technique on grain alignment and grain properties.
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The abstract, sentence by sentence
Thermal dust polarization is a powerful tool to probe magnetic fields ($\textbf{B}$) and grain properties. However, a systematic study of the dependence of dust polarization on grain properties in protostellar environments is not yet available. In this paper, we post-process a non-ideal MHD simulation of a collapsing protostellar core with our updated POLARIS code to study in detail the effects of iron inclusions and grain growth on thermal dust polarization. We found that superparamagnetic (SPM) grains can produce high polarization degree of $p \sim 10-40\%$ beyond $\sim 500$ au from the protostar because of their efficient alignment by magnetically enhanced Radiative Torque mechanism. The magnetic field tangling by turbulence in the envelope causes the decrease in $p$ with increasing emission intensity $I$ as $p\propto I^{\alpha}$ with the slope $\alpha \sim -0.3$. But within 500 au, SPM grains tend to have inefficient internal alignment (IA) and be aligned with $\textbf{B}$ by RATs only, producing lower $p \sim 1\%$ and a steeper slope of $\alpha \sim -0.6$. For paramagnetic (PM) grains, the alignment loss of grains above $1\mu m$ in the inner $\sim 200$ au produces $p << 1\%$ and the polarization hole with $\alpha \sim -0.9$. Grain growth can increase $p$ in the envelope for SPM grains, but cause stronger depolarization for SPM grains in the inner $\sim 500$ au and for PM grains in the entire protostellar core. Finally, we found the increase of polarization angle dispersion function $S$ with iron inclusions and grain growth, implying the dependence of B-field strength measured using the DCF technique on grain alignment and grain properties.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Thermal dust polarization is a powerful tool to probe magnetic fields ($\textbf{B}$) and grain properties. | background 1.00 | 0.05 | 0.02 | asserted 1.00 |
| s1 | However, a systematic study of the dependence of dust polarization on grain properties in protostellar environments is not yet available. | gap 1.00 | 0.04 | 0.02 | asserted 0.99 |
| s2 | In this paper, we post-process a non-ideal MHD simulation of a collapsing protostellar core with our updated POLARIS code to study in detail the effects of iron inclusions and grain growth on thermal dust polarization. | contribution 0.71 | 0.93 | 0.04 | asserted 0.86 |
| s3 | We found that superparamagnetic (SPM) grains can produce high polarization degree of $p \sim 10-40\%$ beyond $\sim 500$ au from the protostar because of their efficient alignment by magnetically enhanced Radiative Torque mechanism. | result 1.00 | 0.95 | 0.32 | asserted 0.99 |
| s4 | The magnetic field tangling by turbulence in the envelope causes the decrease in $p$ with increasing emission intensity $I$ as $p\propto I^{\alpha}$ with the slope $\alpha \sim -0.3$. | result 0.98 | 0.89 | 0.11 | asserted 1.00 |
| s5 | But within 500 au, SPM grains tend to have inefficient internal alignment (IA) and be aligned with $\textbf{B}$ by RATs only, producing lower $p \sim 1\%$ and a steeper slope of $\alpha \sim -0.6$. | result 1.00 | 0.95 | 0.12 | asserted 0.97 |
| s6 | For paramagnetic (PM) grains, the alignment loss of grains above $1\mu m$ in the inner $\sim 200$ au produces $p << 1\%$ and the polarization hole with $\alpha \sim -0.9$. | result 1.00 | 0.93 | 0.09 | asserted 1.00 |
| s7 | Grain growth can increase $p$ in the envelope for SPM grains, but cause stronger depolarization for SPM grains in the inner $\sim 500$ au and for PM grains in the entire protostellar core. | result 1.00 | 0.93 | 0.19 | asserted 0.97 |
| s8 | Finally, we found the increase of polarization angle dispersion function $S$ with iron inclusions and grain growth, implying the dependence of B-field strength measured using the DCF technique on grain alignment and grain properties. | interpretation 0.67 | 0.96 | 0.28 | asserted 0.84 |
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The paper
Original abstract
Thermal dust polarization is a powerful tool to probe magnetic fields ($\textbf{B}$) and grain properties. However, a systematic study of the dependence of dust polarization on grain properties in protostellar environments is not yet available. In this paper, we post-process a non-ideal MHD simulation of a collapsing protostellar core with our updated POLARIS code to study in detail the effects of iron inclusions and grain growth on thermal dust polarization. We found that superparamagnetic (SPM) grains can produce high polarization degree of $p \sim 10-40\%$ beyond $\sim 500$ au from the protostar because of their efficient alignment by magnetically enhanced Radiative Torque mechanism. The magnetic field tangling by turbulence in the envelope causes the decrease in $p$ with increasing emission intensity $I$ as $p\propto I^{\alpha}$ with the slope $\alpha \sim -0.3$. But within 500 au, SPM grains tend to have inefficient internal alignment (IA) and be aligned with $\textbf{B}$ by RATs only, producing lower $p \sim 1\%$ and a steeper slope of $\alpha \sim -0.6$. For paramagnetic (PM) grains, the alignment loss of grains above $1\mu m$ in the inner $\sim 200$ au produces $p << 1\%$ and the polarization hole with $\alpha \sim -0.9$. Grain growth can increase $p$ in the envelope for SPM grains, but cause stronger depolarization for SPM grains in the inner $\sim 500$ au and for PM grains in the entire protostellar core. Finally, we found the increase of polarization angle dispersion function $S$ with iron inclusions and grain growth, implying the dependence of B-field strength measured using the DCF technique on grain alignment and grain properties.
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How the literature uses it
2 arXiv papers cite this in 18 sentences
Papers citing it · 16 sentences without a confident label
Cites it as support 1 paper
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Another issue inside the disk is that our model always points out the poor magnetic alignment for micron-sized and VLGs regardless of grain properties and alignment mechanisms ( [ref] , [ref] ).
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 · Issue of polarized emission from magnetically aligned dust grains · 0.97
What it cites · 5 sentences without a confident label
Cites as background 2 papers
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The most popular technique to measure magnetic fields in protostellar environments is to use polarized thermal dust emission (see, e.g., [ref] , [ref] for recent reviews).
Magnetic fields in star formation: from clouds to cores · Introduction · 0.91
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Magnetic fields ($$) are thought to play an essential role in the collapse of dense cores and the formation of protostar, protostellar disks and planetary systems ( [ref] , [ref] , [ref] , [ref] ).
The role of magnetic fields in the formation of protostars, disks, and outflows · Introduction · 0.94
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