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MAPPING DARK NEBULAE IN ELLIPTICAL GALAXIES.

The Kitt Peak National Observatory video camera has been used on the 2.1-m telescope to provide imaging data for a survey of dark nebulae in 15 classical elliptical galaxies. Dark nebulae in ellipticals trace cool, dense interstellar matter and are potential sites for star formation. Spatial filtering techniques allow previously known dark nebulae in NGC 404, NGC 708, NGC 1052, NGC 4374, NGC 5363, and NGC 7052 to be readily mapped from the digital images. An extended dark nebular component is also found in NGC 5363. The majority of classical ellipticals in the sample, however, do not contain large dark nebulae. These observations are discussed in terms of processes which might control the amount and distribution of cool gas in elliptical galaxies. In particular, the presence of dust suggests that some of the gas has not been heated to the high temperatures characteristic of the X-ray emitting atmospheres that are found in many elliptical galaxies.