Polarized dust emission of magnetized molecular cloud cores

Abstract

We compute polarization maps for molecular cloud cores modeled as magnetized singular isothermal toroids, under the assumption that the emitting dust grains are aspherical and aligned with the large-scale magnetic field. We show that, depending on the inclination of the toroid with the line-of-sight, the bending of the magnetic field lines resulting from the need to counteract the inward pull of gravity naturally produces a depolarization effect toward the centre of the map. We compute the decrease of polarization degree with increasing intensity for different viewing angles and frequencies, and we show that an outward increasing temperature gradient, as expected in starless cores heated by the external radiation field, enhances the decrease of polarization. We compare our results with recent observations, and we conclude that this geometrical effect, together with other mechanisms of depolarization, may significantly contribute to the decrease of polarization degrees with intensity observed in the majority of molecular cloud cores. Finally, we consider the dependence of the polarization degree on the dust temperature gradient predicted for externally heated clouds, and we briefly comment on the limits of the Chandrasekhar-Fermi formula to estimate the magnetic field strength in molecular cloud cores.

15 pages, 9 figures. Astronomy and Astrophysics, in press

References in corpus (16)

• Tracing the Mass during Low-Mass Star Formation. II. Modelling the Submillimeter Emission from Pre-Protostellar Cores
• Radiative Torques on Interstellar Grains: I. Superthermal Spinup
• Radiative Torques on Interstellar Grains: II. Grain Alignment
• SCUBA Polarization Measurements of the Magnetic Field Strengths in the L183, L1544, and L43 Prestellar Cores
• First Observations of the Magnetic Field Geometry in Pre-stellar Cores
• Theoretical Models of Polarized Dust Emission from Protostellar Cores
• The dust temperature distribution in prestellar cores
• High Resolution Millimeter-Wave Mapping of Linearly Polarized Dust Emission: Magnetic Field Structure in Orion
• Polarized Sub-Millimetre Emission from Filamentary Molecular Clouds
• On the efficiency of grain alignment in dark clouds
• Interferometric Mapping of Magnetic Fields in Star-forming Regions III. Dust and CO polarization in DR21(OH)
• Magnetic Fields in Star-Forming Molecular Clouds II. The Depolarization Effect in the OMC-3 Filament of Orion A
• Magnetic Fields in Star-Forming Molecular Clouds. V. Submillimeter Polarization of the Barnard 1 Dark Cloud
• Magnetic field evolution in Bok globules
• Magnetic Fields in Star-Forming Molecular Clouds I. The First Polarimetry of OMC-3 in Orion A
• Monte Carlo radiative transfer in molecular cloud cores

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