THE DIFFUSE GALACTIC EMISSION AT 6.2 MU-M

We present the observation of the 6.2 mum emission toward the inner ga lactic disk, obtained with the AROME balloon-borne experiment with an angular resolution of 0.9-degrees. The galactic coordinates of the obs erved region are -5-degrees less-than-or-equal-to LII less-than-or-equ al-to 35-degrees and -6-degrees less-than-or-equal-to BII less-than-or -equal-to 6-degrees. The measurements reveal the existence of an emiss ion feature at 6.2 mum all over this region. The averaged 6.2 mum surf ace brightness (-1-degrees less-than-or-equal-to BII less-than-or-equa l-to 1-degrees, 8-degrees less-than-or-equal-to LII less-than-or-equal -to 35-degrees) is lambdaI(lambda) = (1.2 +/- 0.3) 10(-5) W/m2/sr with a continuum lambdaI(lambda) = (5.9 +/- 1.2) 10(-6) W/m2/sr and a feat ure intensity DELTA lambdaI(lambda) = (6.1 +/- 1.3) 10(-7) W/m2/sr. If we take into account the effect of dust extinction along the line of sight, we obtain respectively for the 6.2 mum to 3.3 mum emission feat ure ratio and the 6.2 mum feature to 12 mum emissivity ratio: DELTA la mbdaI(lambda)(6.2)/DELTA lambdaI(lambda) (3.3) = 9 +/- 2 and DELTA lam bdaI(lambda) (6.2)/lambdaI(lambda) (12) = 0.09 +/- 0.02; these color r atios are similar to those obtained on UV excited nebulae, despite ver y different radiation field intensities and spectra. We show that the 6.2 mum 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 like PAHs, as it was origi nally proposed by Puget et al. (1985).