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

TL;DR

This study reports the first detection of unidentified infrared emission bands in the disk of an external galaxy, NGC 891, revealing similarities to the Milky Way and some variations along the galaxy's major axis.

Contribution

First observation of UIR bands in an external galaxy's disk, showing similarities to the Milky Way and highlighting spatial variations.

Findings

UIR bands contribute ~9% of total IR radiation in NGC 891

Band ratios and widths are similar to Milky Way's diffuse emission

Notable variations in band ratios along the galaxy's major axis

Abstract

The spectrum of the unidentified infrared (UIR) emission bands between 5.9 and 11.7 [micro]m has been observed for the first time in the disk of an external galaxy. We have used the low-resolution spectrometer of the ISOPHOT instrument aboard ISO. The UIR bands at 6.2, 7.7 and 11.3 [micro]m have absolute intensities which are similar to the values observed for the diffuse emission of our own Galaxy. The UIR bands between 5.9 and 11.7 [micro]m contribute ~9% of the total IR radiation of NGC 891. The intensity ratios and band widths in the NGC 891 disk emissions are similar to the diffuse emission of the Milky Way, pointing to a common carrier for the UIR bands in the two galaxies. However, there are some notable variations of the band ratios along the major axis of the galaxy.