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J.N. Bregman, A.E. Athey (U. Michigan), J.D. Bregman, P. Temi (NASA Ames Research Center)
Early-type galaxies should exhibit thermal emission from the dust that is shed through stellar mass loss and heated by the ambient photon field. Because this emission can give us direct insight into galactic stellar mass loss and the radiation field, we conducted a program to search for this emission with CAM on ISO. We obtained 6-15um imaging observations (3.2' FOV and 6" pixels) in six narrow bands (lw4-9) for the galaxies NGC 1344, NGC 1404, NGC 4636, NGC 4649, NGC 5846, and NGC 7507. Every galaxy is detected in every band and for wavelengths shorter than 9um, thermal emission from stars dominates the spectrum. However, in the 11um band, every galaxy displays excess emission, which cannot be attributed to PAHs because emission in the stronger 7.7um band is not detected. To study this feature in detail, we obtained CVF data from ISOCAM on one source, NGC 1404, which clearly shows broad emission band from 9um to 14um, peaking in the 9.5-11.3um region. It might be possible to explain this surprising result as emission from silicates or SiC. Additional constraints on the origin of this emission is obtained by comparing the spatial distribution of the emission with the distribution of the stellar light, and this will be presented.