Astron. Astrophys. 324, L13-L16 (1997)

4. Conclusion

The present analysis is in qualitative agreement with the predictions that can be made from detailed mid-IR studies of interstellar matter in Galaxy. In spiral and irregular galaxies, the integrated emission around 7 µm is almost entirely due to the carriers of the UIBs ("PAHs"). The integrated emission at 15 µm is also dominated by PAHs in late-type galaxies with a low SFR, but the very small grains (Désert et al.   1990) give a important contribution in high SFR, lower-mass, late-type spirals and irregulars. The emission at both 6.75 and 15 µm is not proportional to the star formation rate for the latter galaxies, probably due to a strongly decreasing amount of both PAHs and perhaps also of very small grains: we suggest that this decrease corresponds to different properties of PAHs in high-SFR, low-metallicity galaxies.

The mid-IR emission of a few early-type galaxies observed serendipitously in our sample is dominated by stars.

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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