Multiscale Synthetic observations of Polarized dust emission: On the origin of Depolarization effect from Molecular clouds to Starless cores and Constraints on Dust Physics
Abstract
Submillimeter observations of polarized dust emission from molecular clouds to starless cores frequently report a decrease in polarization fraction (p) with increasing dust emission intensity (I). This feature is commonly attributed to the alignment loss of dust grains or the geometrical effects of magnetic fields, yet, the detailed contributions remain unclear. To investigate the mechanism responsible for the depolarization, we use POLARIS to perform the multiscale synthetic dust polarization observations at 850μm from magnetically aligned dust grains by RAdiative Torques (RATs) mechanism. We adopt three collapsing cloud models with different magnetic energy levels and explore the effects of grain magnetic properties and grain growth on dust polarization. The field geometrical effect is the dominant depolarization mechanism at NH<1021−1022cm−2. We find that if grains grow beyond >0.5μm and are superparamagnetic (SPM) with large iron clusters, RATs remain effective at high column densities, and grain alignment loss contributes to depolarization only at NH > 1023cm−2. If neither of these conditions is satisfied, the alignment loss (in cases of insufficient grain growth); or the reduced grain alignment efficiency by gaseous damping (for paramagnetic grains or SPM grains with small iron cluster sizes) can become the dominant depolarization mechanism at NH > 1022cm−2, regardless of how tangled the magnetic field lines in our simulation. Finally, we show that the depolarization mechanism and the underlying dust physical properties inside starless cores may be identified through the p−I slope and the mean p at the core center.
Versions
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BibTeX
@misc{giang2026multiscale,
title = {{Multiscale Synthetic observations of Polarized dust emission: On the origin of Depolarization effect from Molecular clouds to Starless cores and Constraints on Dust Physics}},
author = {Nguyen Chau Giang and Thiem Hoang and Blakesley Burkhart and Doris Arzoumanian and Nguyen Bich Ngoc and Jihye Hwang and Aran Lyo},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.30009},
eprint = {2608.30009},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.30009},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Multiscale Synthetic observations of Polarized dust emission: On the origin of Depolarization effect from Molecular clouds to Starless cores and Constraints on Dust Physics
AU - Nguyen Chau Giang
AU - Thiem Hoang
AU - Blakesley Burkhart
AU - Doris Arzoumanian
AU - Nguyen Bich Ngoc
AU - Jihye Hwang
AU - Aran Lyo
PY - 2026
DA - 2026/08/30
PB - arXiv
DO - 10.48550/arxiv.2608.30009
UR - https://arxiv.org/abs/2608.30009
AB - Submillimeter observations of polarized dust emission from molecular clouds to starless cores frequently report a decrease in polarization fraction (p) with increasing dust emission intensity (I). This feature is commonly attributed to the alignment loss of dust grains or the geometrical effects of magnetic fields, yet, the detailed contributions remain unclear. To investigate the mechanism responsible for the depolarization, we use POLARIS to perform the multiscale synthetic dust polarization observations at 850μm from magnetically aligned dust grains by RAdiative Torques (RATs) mechanism. We adopt three collapsing cloud models with different magnetic energy levels and explore the effects of grain magnetic properties and grain growth on dust polarization. The field geometrical effect is the dominant depolarization mechanism at N_H<10^21−10^22cm^−2. We find that if grains grow beyond >0.5μm and are superparamagnetic (SPM) with large iron clusters, RATs remain effective at high column densities, and grain alignment loss contributes to depolarization only at N_H > 10^23cm^−2. If neither of these conditions is satisfied, the alignment loss (in cases of insufficient grain growth); or the reduced grain alignment efficiency by gaseous damping (for paramagnetic grains or SPM grains with small iron cluster sizes) can become the dominant depolarization mechanism at N_H > 10^22cm^−2, regardless of how tangled the magnetic field lines in our simulation. Finally, we show that the depolarization mechanism and the underlying dust physical properties inside starless cores may be identified through the p−I slope and the mean p at the core center.
ER -