The anomalous foreground was detected 10 years ago as an unexpected Galactic screen at cm-wavelengths in experiments designed to map the Cosmic Microwave Background (CMB), seen in the direction of cirrus interstellar dust clouds and ubiquitous at high Galactic latitudes. A joint Universidad de Chile (U. Ch.) and Caltech effort led to the discovery of surprisingly bright radio emission from canonical dark (i.e. dusty) clouds: rho Oph and M78, as well as translucent LDN1780 and zeta Oph. What is the nature of the cm-wave emitters? Do the dark clouds and the cirrus clouds radiate by the same emission mechanisms? The identification of the cm-wave sources is required to inform the subtraction of diffuse Galactic foregrounds from CMB polarization experiments. It may also provide a new diagnostic of the interstellar medium (ISM). The data on well studied local clouds can bring information on the environments giving rise to cm-wave radiation. The U. Ch. participant seeks to collaborate with the ISM team at the LUTh laboratory of the Observatoire de Paris, who has an established expertise on the theoretical modelling of ISM physical conditions. We aim at distinguishing between two broad interpretations of the cm-wave emission, based either on unexpected physical conditions, or a new astrophysical process: 1- Cold plasma radiation due to residual charges in molecular gas, such as CI continuum from the external layers (the photo-dissociation-regions) of clouds exposed to interstellar soft-UV radiation. If confirmed the CI continuum would trace unexpectedly dense and clumpy molecular gas in regions of intermediate-mass star formation. 2-The exciting possibility of spinning dust emission, which may provide the first direct probe of interstellar very small grains (such as polycyclic aromatic ydrocarbons). These poorly understood dust grains play a crucial role in the thermal and chemical balance of the atomic/molecular ISM.
Field of science
- /agricultural sciences/agriculture, forestry, and fisheries/agriculture/grains and oilseeds
- /natural sciences/physical sciences/astronomy/planetary science/celestial mechanics
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