Mid-Infrared Emission Features in the ISM: Feature-to-Feature Flux Ratios
N. Y. Lu;
ApJ, 1998, 498, L65
ABSTRACT:Using a limited but representative sample of sources in the interstellar medium of our Galaxy with published spectra from the Infrared Space
Observatory, we analyze the flux ratios between the major mid-IR emission features
(EFs) centered around 6.2, 7.7, 8.6, and 11.3 mu m, respectively.
In a flux
ratio-to-flux ratio plot of EF(6.2 mu m)/EF(7.7 mu m) as a function of EF(11.3 mu
m)/EF(7.7 mu m), the sample sources form roughly a Lamda -shaped locus that
appears to trace, on an overall basis, the hardness of a local heating radiation
field.
But some driving parameters other than the radiation field may also be
required for a full interpretation of this trend.
On the other hand, the flux
ratio of EF(8.6 mu m)/EF(7.7 mu m) shows little variation over the sample
sources, except for two H II regions that have much higher values for this ratio
because of an "EF(8.6 mu m) anomaly," a phenomenon clearly associated with
environments of an intense far-UV radiation field.
If further confirmed on a larger
database, these trends should provide crucial information on how the EF carriers
collectively respond to a changing environment.
KEYWORDS: infrared: ism: lines and bands, ism: general
PERSOKEY:pah, mir, iso, dust, ,
CODE: lu98