Unidentified infrared emission bands and sub-micron dust grains in the diffuse interstellar medium

Details Unidentified infrared emission bands and sub-micron dust grains in the diffuse interstellar medium Unidentified infrared emission bands and sub-micron dust grains in the diffuse interstellar medium

Mar 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999esasp.427..731o&link_type=abstract

The Universe as Seen by ISO. Eds. P. Cox & M. F. Kessler. ESA-SP 427., p. 731

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Interstellar Dust, Unidentified Infrared Emission Bands, Hii Regions

Scientific paper

Two H II regions, the Carina nebula and Sharpless 171, and the ρ Oph cloud region, have been mapped with PHT-S and LWS full grating scan (45-170 μm). The unidentified infrared (UIR) emission bands at 6.2, 7.7, 8.6, and 11.2 μm were detected at most observed positions. Their spatial variations are examined in relation to the far-infrared emission from the submicron dust grains. The temperature and optical depth of submicron grains are derived from the fit of the LWS spectra with modified blackbody. The strength of the incident radiation field in units of the solar vicinity value (G0) is estimated from the dust temperature. The ratio of the UIR 7.7 μm band to the total far-infrared intensity (FIR) shows a similar trend in the two H II regions. It decreases as G0 increases for G0 > 1000. The ratio, however, stays constant in the ρ Oph region, even for G0 > 1000. A more general relation is found if the ratio is plotted against [O III] 88 μm line intensity divided by FIR. The plot indicates that the UIR band carrier may be destroyed or the emission mechanism becomes inefficient in ionized regions. On the other hand, the relative band strengths among the UIR bands do not show any systematic trend with the radiation strength or ionization, indicating that the material properties of the UIR band carrier do not vary appreciably with the radiation field.

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