Oral Presentation
What can we learn from the multi-wavelength polarization observations?
Presenter: Chia-Lin Ko (NTHU/ASIAA)
The previous SMA 0.87 mm and CARMA 1.3 mm surveys of dust polarization toward protostars (Galametz et al. 2018; Hull et al. 2014) have shown that polarization percentage in general decreases rapidly with total intensity. They also hinted with a dichotomy that the projected polarization E-segments are either parallel or perpendicular to the outflow axes. Based on the JVLA 18-48 GHz and ALMA 230 and 345 GHz polarization observations towards the specific Class 0 YSO, NGC1333 IRAS4A, we conjectured a unified interpretation of these facts based on aligned dust grains with B-field. At 345 GHz, we found that the radial polarization percentage profiles of IRAS4A1 and IRAS4A2 may be consistent with centrally illuminated collapsing cores, which have an hourglass shaped B-field topology, r^-2 volume density profile, and an approximately consistent grain alignment efficiency. The modestly high optical depth leads to the depolarization at the center of IRAS4A2. The much higher optical depth at the center of IRAS4A1 eventually leads to a 90 degree flip of polarization position angles at 230 and 345 GHz with respect to those observed at 18-48 GHz. At 230 and 345 GHz, what we detected were the linear polarization due to dust extinction instead of dust emission. We conclude that the 230/345 GHz polarization observations towards Class 0 YSOs indeed trace B-field, although any dichotomy related to how E-field is aligned with certain prefer axes (e.g., outflow, filament) may be related to the optical thickness of the selected samples.
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