Work

Multiscale Synthetic Observations of Polarized Dust Emission: On the Origin of Depolarization Effect from Molecular Clouds to Starless Cores and Constraints on Dust Physics

Year: 2026

Type: article

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 the Polarized Radiative Simulator to perform multiscale synthetic dust polarization observations at 850 μ m from magnetically aligned dust grains by the RAdiative Torque (RAT) 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 22 cm −2 . We find that if grains grow beyond >0.5 μ m 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 23 cm −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 22 cm −2 , regardless of how tangled the magnetic field lines are 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.

Source: The Astrophysical Journal

DOI: 10.3847/1538-4357/aea15f