Properties of the Galactic Interstellar Medium Emission
As part of the Hi-GAL project, Paradis et al. (2010) have found an inverse relationship between the dust temperature and the spectral index, shown for the first time in the inner Galactic Plane (GP). The Two-Level Systems (TLS) model (Mény et al., 2007), based on the disordered internal structure of the amorphous dust grains has been developed to interpret observations in the FIR-submm domain, where other models were poorly convincing. A recent work focusing on the comparison between data of the diffuse ISM seen by FIRAS-WMAP, as well as Archeops compact sources, with the new TLS model allowed us to constrain the model parameters characterizing the general Galactic dust properties (Paradis et al., 2011, submitted). Using the newly available Hi-GAL data over 37 fields, we report a 500 μm emissivity excess in the external parts of the GP that can reach 20% of the emissivity. Results of the TLS modeling indicate significant changes in the dust properties from the inner to the external parts of the GP.