|Annu. Rev. Astron. Astrophys. 2000. 38: Copyright © 2000 by .
All rights reserved 5.4. Obscured populations ISO and SCUBA
observations of the HDF and other fields have revealed an
energetically important population of dust-obscured objects.
Interpretation of these results has been the subject of
considerable debate, because of ambiguities in source
identification and in distinguishing starbursts from AGN. The
ISOCAM (6.7 and 15 µm) and SCUBA (850 µm) observations bracket
but do not sample the wavelength regime 100 < p < 200 µm near
the peak of the far-IR emission, making it difficult to assess
reliably the source contribution to the global emissive energy
budget of galaxies. Although strong mid-IR emission accompanies
vigorous star formation in many nearby galaxies, the
unidentified IR emission bands carry most of the energy in the
wavelength range sampled by ISOCAM at z ~ 1. The bulk of re-
emitted radiation, however, emerges near p, and there is
considerable diversity in f (10 µm) / f(100 µm) flux ratios am