Oral Presentation
Physical Modeling of Dust Polarization from Magnetically Enhanced Radiative Torque (MRAT) Alignment in Protostellar Cores with POLARIS [Cancelled]
Presenter: Chau Giang Nguyen (Korea University of Science and Technology (UST), Korea Astronomy and Space Science Institute (KASI))
Magnetic fields (B) are an important factor that controls the star formation process. The leading method to observe B orientation is using polarized thermal emission from dust grains aligned with B. However, in dense environments such as protostellar cores, dust grains may have inefficient alignment due to strong gas randomizations, so that using dust polarization to trace B is uncertain. Hoang & Lazarian (2016) demonstrated that the grain alignment by RAdiative Torques is enhanced if dust grains contain embedded iron inclusions. Here we extend POLARIS code to study the effect of iron inclusions on grain alignment and thermal dust polarization toward a protostellar core, assuming uniform B. We found that paramagnetic grains produce a low polarization degree of p ~ 1% in the envelope and negligible p << 1% in the central region due to the loss of grain alignment. In contrast, grains with a high level of iron inclusions have perfect alignment and produce high $p ~ 40% in the envelope and low p < 10% in the central region. Grains with a moderate level of iron inclusions induce the polarization flipping from P perpendicular to B at millimeter to P parallel to B at submillimeter due to the change in the internal alignment caused by slow internal relaxation. The weak alignment of large grains of a > 10um reduces dichroic extinction efficiency at submillimeter. We found a positive correlation between p(%) and the level of iron inclusions, which opens a new window to constrain the abundance of iron locked in dust through dust polarimetry.
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