Modelling the spinning dust emission from dense interstellar clouds

Abstract

Electric dipole emission arising from PAHs is often invoked to explain the anomalous microwave emission (AME). This assignation is based on an observed tight correlation between the mid-IR emission of PAHs and the AME; and a good agreement between models of spinning dust and the broadband AME spectrum. So far often detected at large scale in the diffuse interstellar medium, the AME has recently been studied in detail in well-known dense molecular clouds with the help of Planck data. While much attention has been given to the physics of spinning dust emission, the impact of varying local physical conditions has not yet been considered in detail. Our aim is to study the emerging spinning dust emission from interstellar clouds with realistic physical conditions and radiative transfer. We use the DustEM code from Compiegne et al. to describe the extinction and IR emission of all dust populations. The spinning dust emission is obtained with SpDust, as described by Silsbee et al., that we have coupled to DustEM. We carry out full radiative transfer simulations and carefully estimate the local gas state as a function of position within interstellar clouds. We show that the spinning dust emission is sensitive to the abundances of the major ions and we propose a simple scheme to estimate these abundances. We also investigate the effect of changing the cosmic-ray rate. In dense media, where radiative transfer is mandatory, we show that the relationship between the spinning and mid-IR emissivities of PAHs is no longer linear and that the spinning dust emission may actually be strong at the centre of clouds where the mid-IR PAH emission is weak. These results provide new ways to trace grain growth from diffuse to dense medium and will be useful for the analysis of AME at the scale of interstellar clouds.

7 pages, 10 figures, accepted by A&A

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• A refined model for spinning dust radiation
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• Centimeter-wave continuum radiation from the rho Ophiuchi molecular cloud
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• A multi-wavelength investigation of RCW175: an HII region harboring spinning dust emission
• TRUST I: A 3D externally illuminated slab benchmark for dust radiative transfer
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• COMAP Early Science: VI. A First Look at the COMAP Galactic Plane Survey
• Confirmation of Enhanced Long Wavelength Dust Emission in OMC 2/3
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• QUIJOTE scientific results -- X. Spatial variations of Anomalous Microwave Emission along the Galactic plane
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• CARMA Observations of Galactic Cold Cores: Searching for Spinning Dust Emission
• QUIJOTE scientific results -- XVIII. New constraints on the polarization of the Anomalous Microwave Emission in bright Galactic regions: $\rho$\,Ophiuchi, Perseus and W43
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