2019 ASROC Annual Meeting
National Museum of Natural Science, Taichung
May 17~19


Resolving linear polarization due to emission and extinction of aligned dust grains on NGC1333 IRAS4A with JVLA and ALMA

[ Oral ]

Chia-Lin Ko (NTHU); Hauyu Baobab Liu (ASIAA); Shih-Ping Lai (NTHU); Tao-Chung Ching (NAOC); Ramprasad Rao (ASIAA); Josep Miquel Girart (CSIC-IEEC)

We report high angular resolution observations of dust linear polarization towards the Class 0 young stellar object (YSO) NGC1333 IRAS4A (hereafter, IRAS4A) using the Karl G. Jansky Very Large Array (JVLA) at K (11.5-16.7 mm), Ka (8.1-10.3 mm), and Q bands (6.3-7.9 mm), and using the Atacama Large Millimeter Array (ALMA) at Band 6 (1.28 mm) and Band 7 (0.85-0.89 mm). On 100-1000 AU scales, all of these observations consistently trace the hourglass shaped magnetic field (B-field) topology as shown in the previous studies. Inner than the 100 AU region of IRAS4A1, the polarization position angles (E-field) detected at 6.3-16.7mm are consistent, however, are nearly 90 degrees offset from those detected at 1.2 mm and 0.85-0.89 mm. Such a 90 degree offset may be explained by that the inner ~100 AU area is optically thick at wavelengths shorter than ~1.5 mm, whereby the observations probe the absorption of aligned dust against the weakly or unpolarized warm dust emission from the innermost region. This can also consistently explain why the highest angular resolution ALMA images at Band 7 show that the polarization percentage increases with dust brightness temperature in the inner ~100 AU region of IRAS4A1. Following this interpretation and assuming that the dust grains are aligned with the magnetic fields, the inferred magnetic field position angle based on the 90 degrees rotated at 6.3-7.9 mm in the central peak of IRAS4A1 is ~-22 degrees, which is approximately consistent with the outflow direction ~-9 degrees.