Tracing Molecular Emission in Spiral Galaxies: The Near Infrared Correspondence

Near infrared imaging can be a powerful tool in tracing the densest molecular structures in galaxies. The observable molecular emission originates in large molecular cloud complexes which are also subject to significant extinctions caused by the associated dust. It can be difficult to distinguish between regions of moderate and large molecular density with optical observations as both will appear optically thick. Since extinction in the near infrared is only about a tenth of the corresponding visual extinction, multi-band near infrared imaging will trace the regions of the highest optical depths much more effectively. With the advent of large format infrared imaging arrays it is now possible to use infrared extinction maps as a probe of the large scale distribution of molecular emission in extragalactic sources.