Speaker
Description
Magnetic fields are a fundamental component of the interstellar medium (ISM), yet they cannot be observed directly and must instead be inferred through indirect tracers. Polarized thermal dust emission is a good tracer of magnetic fields in many ISM conditions, as dust grains are generally expected to be well aligned with the magnetic field. In this work, we investigate the leading theory of grain alignment, Radiative Torque Alignment (RAT), focusing on its prediction of enhanced grain alignment in the vicinity of embedded protostars. While this prediction has been explored through analytical models and magnetohydrodynamic simulations, observational evidence has remained limited. Using 214 μm SOFIA/HAWC+ polarimetric observations of the high-mass star-forming region DR21, we perform a statistical analysis of the polarization fraction, polarization angle dispersion, and grain alignment efficiency to examine this effect near embedded protostars. We find evidence of enhanced polarization near DR21(OH) at intensities where depolarization is typically observed. This conclusion is further strengthened by comparison with predictions from a simple analytical model of a centrally heated envelope surrounding a luminous protostar, which shows good agreement with the observed trends. Our results indicate that grain alignment via radiative torques remains efficient near embedded protostars and that polarized thermal dust emission can therefore be used to probe magnetic fields in the densest regions of star formation.