1994A&A...291L...5B

We present the spectral distribution of dust in the diffuse ISM as derived from the first release of the DIRBE (Diffuse Infrared Background Explorer) data, in the wavelength range from 3.5 to 240µm. Although the spectrum of diffuse regions strongly decreases from 12µm toward shorter wavelengths, it is found that some dust emission is still present in the L and M bands. On average, it corresponds to ∼1% of the total IR emission. The comparison with the 3.3µm Polycyclic Aromatic Hydrocarbon (PAH) feature emissivity of the diffuse medium in the inner galaxy shows that only a small fraction (8-16%) of the DIRBE L band ISM emission is likely to be produced by the 3.3µm feature. Along with the presence of an important dust emission in the DIRBE; M band, where no PAH feature is expected, this implies that a continuum component and/or other features from dust also contribute significantly to the short wavelength emission. The carrier of this emission still has to be identified. Large color variations are observed from region to region over most of the DIRBE range, which might reflect abundance variations of the various dust components.