Constraining Dust Properties and Dust Dynamic in the era of ALMA dust polarization

ABSTRACT :
Polarized dust emission from magnetically aligned dust grains is a powerful tool for tracing the plane-of-sky magnetic field (B), probing dust physics, and testing grain alignment theory. The magnetic alignment of dust grains toward dense environments as protostellar cores is expected to be inefficient due to the high gas randomization effect, but how bad it behaves, how strong it affects dust polarization properties, and whether dust polarization observed in the core scale still trace B fields are not well quantified. Besides, dust grains subjected to intense stellar radiation sources could be disrupted by RAdiative Torques Disruption (RATD), but their realistic influence on dust population and dust polarization is unclear. To access these questions, we perform synthetic dust polarization modeling of MHD simulations of intermediate-mass YSO using our updated POLARIS code. The result is then post-processed with CASA and compared with ALMA observation to accurately constrain the grain physics and grain properties in protostellar environments. We found that in the envelope scale, dust grains with embedded Ncl~5-1e4 iron atoms/clusters (thus be superparamagnetic material, SPM) can achieve perfect alignment with magnetic fields by the joint action of super-Barnett relaxation and Magnetically enhanced RAdiative Torques (MRAT) mechanism, which reproduces well the wide dynamic range of high p~5-40% observed by ALMA there. But to reproduce p ~ 1 - 8% observed in the inner envelope and disk scale, significant grain growth, higher Ncl ~ 1e2-1e4 embedded inside SPM grains, and especially Inelastic relaxation mechanism, are required to maintain the considerable alignment range and efficient internal and external magnetic alignment from sub-micron to very large grains (VLGs) of 10-50um. We indicated that the reduction of the alignment degree of VLGs with increasing gaseous damping is the major origin producing the depolarization effect inside low/intermediate YSOs. On the other hand, we find that during the accretion burst event, RATD can stop temporarily the transportation of micron-sized/VLGs/submillimeter grains from disks to inner envelope as proposed by Wong et al. (2016) and Tsukamoto et al. (2021), and let sub-micron/small micron-sized grains of ~1-3um be the major dust population inside outflow cavities. The suppression of RATD on dust polarization may be recognized via the uniform dust polarization degree distribution from the outflow cavity wall to the equatorial midplane, only if dust grains have very high porous, aggregate-gate structure with low maximum tensile strength Smax < 1e5ergcm-3.