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Structure Generation by Irradiation: What can GLIMPSE teach us about the ISM structure?

F. Heitsch·B. Whitney·R. Indebetouw·M. R. Meade·B. L. Babler·E. Churchwell·;
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Abstract

Diffuse emission in the mid-infrared shows a wealth of structure, that lends itself to high-resolution structure analysis of the interstellar gas. A large part of the emission comes from polycyclic aromatic hydrocarbons, excited by nearby ultra-violet sources. Can the observed diffuse emission structure be interpreted as column density structure? We discuss this question with the help of a set of model molecular clouds bathed in the radiation field of a nearby O-star. The correlation strength between column density and ``observed'' flux density strongly depends on the absolute volume density range in the region. Shadowing and irradiation effects may completely alter the appearance of an object. Irradiation introduces additional small-scale structure and it can generate structures resembling shells around HII-regions in objects that do not possess any shell-like structures whatsoever. Nevertheless, structural information about the underlying interstellar medium can be retrieved. In the more diffuse regime ($n({HI})\lesssim 100$cm$^{-3}$), flux density maps may be used to trace the 3D density structure of the cloud via density gradients. Thus, while caution definitely is in order, mid-infrared surveys such as GLIMPSE will provide quantitative insight into the turbulent structure of the interstellar medium.

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F. Heitsch, B. Whitney, R. Indebetouw, M. R. Meade, B. L. Babler, E. Churchwell, ;. 2006-07-14. Structure Generation by Irradiation: What can GLIMPSE teach us about the ISM structure?. https://doi.org/10.1086/510522

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