B-fields And dust in interstelLar fiLAments using Dust POLarization (BALLAD-POL): II. Testing the Radiative Torque Paradigm in Musca and OMC-1

Polarization of starlight and thermal dust emission caused by aligned dust grains is a valuable tool to characterize magnetic fields (B-fields) and constrain dust properties. However, the physics of grain alignment is not fully understood. To test the popular paradigm of radiative torque (RAT) theory, including RAT alignment (RAT-A) and disruption (RAT-D), we use dust polarization data observed by Planck and SOFIA/HAWC+ toward two filaments with contrasting physical conditions: Musca, a quiet filament, and OMC-1, a highly dynamic filament due to feedback. We analyze various relations of the observed polarization fraction, P, with gas column density, , dust temperature, , and polarization angle dispersion function, . We found that P decreases with increasing and increasing , as expected from RAT-A. On the other hand, the P- relation is more complicated; it is a linear correlation at low but turns into an anti-correlation when reaches a certain high value. Next, we compute the polarization fraction on a pixel-by-pixel with B-fields in the plane of the sky using the DustPOL code based on RAT, incorporate the depolarization effect by B-field tangling using , and compare the realistic polarization model with observations of Musca and OMC-1. For Musca with well-ordered B-fields, our numerical model reproduces the decline of P toward the filament spine (aka. polarization hole), having high and low , indicating the loss of grain alignment efficiency due to RAT-A. For OMC-1, with stronger B-field variations and higher , our model can reproduce the observed P- and P-N( H_2) relations only if the depolarization effect resulting from B-field tangling and RAT-D effect are taken into account. Our results provide more robust observational evidence for the RAT paradigm, particularly the recently discovered RAT-D.