SIMBAD references

We present new data obtained with the French balloon-borne instrument AROME, concerning the general emission of the Galaxy at 3.3µm : continuum and emission feature. Maps of the galactic plane are presented for galactic longitudes -60deg< LII < 60deg and latitudes -5deg< BII < 5deg. The continuum shows the exponential disk plus bulge stellar distributions, and the feature shows the thin dust disk. We show that, at large scale, the variations of the 3.3µm-feature/100µm and 12µm/100µm ratios can be interpreted in terms of extinction along the line of sight. We derive the following generic galactic dust colors for the diffuse medium: {DELTA}{lambda.epsilon_lambda}(3.3µm-feature)/{lambda.epsilon_lambda}(100) = 2.5±0.4 10^–3, and {lambda.epsilon_lambda}(12)/{lambda.epsilon_lambda}(100) = 0.31±0.03. We show that there is no evidence for large scale variations of these colors, neither with the galactocentric distance, nor with the nature of the gas in which the emitting dust is located, neutral or molecular. This is interpreted as a strong argument in favor of a universal galactic mixture of dust grains. We show that the value of the 12/100 ratio can only be explained with a dust model including large molecules a few Angstroems size. The observation of the 3.3µm feature indicates that a significant fraction of these molecules may be Polycyclic Aromatic Hydrocarbons (PAHs). In this hypothesis, our results imply a homogeneous mixing of the PAHs into the general interstellar medium and a mass abundance of 3 to 8 % of the cosmic carbon. We show that these observational facts are marginally compatible with the hypothesis of mass-losing carbon stars being the main sites of PAH production in the Galaxy. We suggest that direct formation of PAHs in interstellar clouds may also occur.