1994A&A...286L..23R

We present the observation of the 6.2 µm emission toward the inner galactic disk, obtained with the AROME balloon-borne experiment with an angular resolution of 0.9 deg. The galactic coordinates of the observed region are -5deg =< L II =< 35deg and -6deg =< B II =< 6deg. The measurements reveal the existence of an emission feature at 6.2µm all over this region. The averaged 6.2µm surface brightness (-1deg =< B II =< 1deg, 8deg =< L II =< 35deg) is λI_λ=(1.2±0.3)10^–5W/m²/sr with a continuum λI_λ=(5.9±1.2)1O^–6W/m²/sr and a feature intensity {DELTA}λI_λ=(6.1±1.3)10^–7W/m²/sr. If we take into account the effect of dust extinction along the line of sight, We obtain respectively for the 6.2µm to 3.3µm emission feature ratio and the 6.2µm feature to 12µm emissivity ratio: {DELTA}λI_λ(6.2)/{DELTA}λI_λ(3.3)=9±2 and {DELTA}λI_λ(6.2)/{DELTA}λI_λ(12)=0.09±0.02; these color ratios are similar to those obtained on UV excited nebulae, despite very different radiation field intensities and spectra. We show that the 6.2µm emission can only arise from the diffuse interstellar medium. In consequence, it supports an emission process involving transiently heated very small grains or large molecules lilk PAHs, as it was originally proposed by Puget et al. (1985).