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  1. Abstract

    The heart of the Large Magellanic Cloud, 30 Doradus, is a complex region with a clear core-halo structure. Feedback from the stellar cluster R136 has been shown to be the main source of energy creating multiple parsec-scale expanding-shells in the outer region, and carving a nebula core in the proximity of the ionization source. We present the morphology and strength of the magnetic fields (B-fields) of 30 Doradus inferred from the far-infrared polarimetric observations by SOFIA/HAWC+ at 89, 154, and 214μm. TheB-field morphology is complex, showing bending structures around R136. In addition, we use high spectral and angular resolution [Cii] observations from SOFIA/GREAT and CO(2-1) from APEX. The kinematic structure of the region correlates with theB-field morphology and shows evidence of multiple expanding-shells. OurB-field strength maps, estimated using the Davis–Chandrasekhar–Fermi method and structure-function, show variations across the cloud within a maximum of 600, 450, and 350μG at 89, 154, and 214μm, respectively. We estimated that the majority of the 30 Doradus clouds are subcritical and sub-Alfvénic. The probability distribution function of the gas density shows that the turbulence is mainly compressively driven, while the plasma beta parameter indicates supersonic turbulence. We show that theB-field is sufficient to hold the cloud structure integrity under feedback from R136. We suggest that supersonic compressive turbulence enables the local gravitational collapse and triggers a new generation of stars to form. The velocity gradient technique using [Cii] and CO(2-1) is likely to confirm these suggestions.

     
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  2. Abstract The alignment of dust grains with the ambient magnetic field produces polarization of starlight as well as thermal dust emission. Using the archival SOFIA/HAWC+ polarimetric data observed toward the ρ Ophiuchus (Oph) A cloud hosted by a B star at 89 and 154 μ m, we find that the fractional polarization of thermal dust emission first increases with the grain temperature and then decreases once the grain temperature exceeds ≃25–32 K. The latter trend differs from the prediction of the popular RAdiative Torques (RATs) alignment theory, which implies a monotonic increase of the polarization fraction with the grain temperature. We perform numerical modeling of polarized dust emission for the ρ Oph-A cloud and calculate the degree of dust polarization by simultaneously considering the dust grain alignment and rotational disruption by RATs. Our modeling results could successfully reproduce both the rising and declining trends of the observational data. Moreover, we show that the alignment of only silicate grains or a mixture of silicate–carbon grains within a composite structure can reproduce the observational trends, assuming that all dust grains follow a power-law size distribution. Although there are a number of simplifications and limitations to our modeling, our results suggest grains in the ρ Oph-A cloud have a composite structure, and the grain size distribution has a steeper slope than the standard size distribution for the interstellar medium. Combination of SOFIA/HAWC+ data with JCMT observations 450 and 850  μ m would be useful to test the proposed scenario based on grain alignment and disruption by RATs. 
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