Detection of widely distributed UIR band emission in the disk of NGC 891

The spectrum of the unidentified infrared (UIR) emission bands between 5.9 and 11.7 mu m has been observed for the first time in the disk of an extern al galaxy. We have used the low-resolution spectrometer of the ISOPHOT inst rument aboard ISO. The UIR bands at 6.2, 7.7, 8.6, and 11.3 mu m have absol ute intensities which are similar to the values observed for the diffuse em ission of our own Galaxy. The UIR bands between 5.9 and 11.7 mu m contribut e similar to 9% of the total IR radiation of NGC 891. The intensity ratios and band widths in the NGC 891 disk emission are similar to the diffuse emi ssion of the Milky Way, pointing to a common carrier for the UIR bands in t he two galaxies. However, there are some notable variations of the band rat ios along the major axis of the galaxy.