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Variations in the abundance of small particles

Published online by Cambridge University Press:  03 August 2017

F. Boulanger
F. Boulanger*
Affiliation:
Radioastronomie, Ecole Normale Supérieure, 24 rue Lhomond, 75005 Paris, France

Abstract

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IRAS images of nearby molecular clouds show that the mid-IR emission from small particles in the size range 102 to 105 atoms is distributed very differently from the 100 μm emission from large dust grains. Variations in color ratios by as much as one order of magnitude are seen on all angular scales. We summarize observational properties of the color variations and argue that neither their large amplitude nor their morphology can be explained by changes of the excitation by the UV radiation field only. The color variations reflect considerable inhomogeneities in the abundance of small particles. We suggest that the abundance variations are related to the cycling of interstellar matter between the gas phase and dust grains. This interpretation entails that clouds with distinct IR colors differ in their density and velocity structure and that cycling of matter between gas phase and dust grains is more ubiquitous and rapid that generally thought.

Keywords

Molecular CloudsGrains : Size DistributionIR EmissionIRAS Colors
Type
Chemistry
Information
Symposium - International Astronomical Union , Volume 147: Fragmentation of Molecular Clouds and Star Formation , 1991 , pp. 151 - 160
Copyright
Copyright © Kluwer 1991 

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