Understanding the Multi-wavelength Thermal Dust Polarization from the Orion Molecular Cloud in Light of the Radiative Torque Paradigm
Le Ngoc Tram, Thiem Hoang, Helmut Wiesemeyer, Isabelle Ristorcelli, Karl M. Menten, Nguyen Bich Ngoc, Pham Ngoc Diep
arXiv:2403.17088v1 Announce Type: new
Abstract: Dust grains are important in various astrophysical processes and serve as indicators of interstellar medium structures, density, and mass. Understanding their physical properties and chemical composition is crucial in astrophysics. Dust polarization is a valuable tool for studying these properties. The Radiative Torque (RAT) paradigm, which includes Radiative Torque Alignment (RAT-A) and Radiative Torque Disruption (RAT-D), is essential to interpret the dust polarization data and constrain the fundamental properties of dust grains. However, it has been used primarily to interpret observations at a single wavelength. In this study, we analyze the thermal dust polarization spectrum obtained from observations with SOFIA/HAWC+ and JCMT/POL-2 in the OMC-1 region and compare the observational data with our numerical results using the RAT paradigm. We find that the dense gas exhibits a positive spectral slope, whereas the warm regions show a negative one. We demonstrate that a one-layer dust (one-phase) model can only reproduce the observed spectra at certain locations and cannot match those with prominent V-shape spectra (for which the degree of polarization initially decreases with wavelength from 54 to $sim$ 300$,mu$m and then increases at longer wavelengths). To address this, we improve our model by incorporating two dust components (warm and cold) along the line of sight, resulting in a two-phase model. This improved model successfully reproduces the V-shaped spectra. The best model corresponds to a mixture composition of silicate and carbonaceous grains in the cold medium. Finally, by assuming the plausible model of grain alignment, we infer the inclination angle of the magnetic fields in OMC-1. This approach represents an important step toward better understanding the physics of grain alignment and constraining 3D magnetic fields using dust polarization spectrum.arXiv:2403.17088v1 Announce Type: new
Abstract: Dust grains are important in various astrophysical processes and serve as indicators of interstellar medium structures, density, and mass. Understanding their physical properties and chemical composition is crucial in astrophysics. Dust polarization is a valuable tool for studying these properties. The Radiative Torque (RAT) paradigm, which includes Radiative Torque Alignment (RAT-A) and Radiative Torque Disruption (RAT-D), is essential to interpret the dust polarization data and constrain the fundamental properties of dust grains. However, it has been used primarily to interpret observations at a single wavelength. In this study, we analyze the thermal dust polarization spectrum obtained from observations with SOFIA/HAWC+ and JCMT/POL-2 in the OMC-1 region and compare the observational data with our numerical results using the RAT paradigm. We find that the dense gas exhibits a positive spectral slope, whereas the warm regions show a negative one. We demonstrate that a one-layer dust (one-phase) model can only reproduce the observed spectra at certain locations and cannot match those with prominent V-shape spectra (for which the degree of polarization initially decreases with wavelength from 54 to $sim$ 300$,mu$m and then increases at longer wavelengths). To address this, we improve our model by incorporating two dust components (warm and cold) along the line of sight, resulting in a two-phase model. This improved model successfully reproduces the V-shaped spectra. The best model corresponds to a mixture composition of silicate and carbonaceous grains in the cold medium. Finally, by assuming the plausible model of grain alignment, we infer the inclination angle of the magnetic fields in OMC-1. This approach represents an important step toward better understanding the physics of grain alignment and constraining 3D magnetic fields using dust polarization spectrum.