Detection of the mid-infrared unidentified bands in the diffuse galactic emission by IRTS

This letter presents the first results of the mid-infrared spectrum (4.5-11.7 mu m) of the diffuse emission near to the galactic plane (l similar to 50 degrees; \b\ less than or equal to 5 degrees) obtained by the mid-infrared spectrometer on board the Infrared Telescope in Space mission. The results clearly demonstrate the presence of unidentified infrared emission (UIR) bands at 6.2, 7.7, 8.6, and 11.3 mu m in the diffuse galactic emission. The distribution of the UIR bands correlates well with the IRAS 100 mu m map, suggesting that the UIR-band emitting material is well mixed with the classical dust grains in general interstellar space. The present results indicate that more than 70% of the IRAS 12 mu m flux diffuse emission is emitted in the spectral range 8-11.7 mu m, and that most of the 12 mu m excess comes from the features associated with the UIR bands.