The following document lists the file abstract/GHELOU_HI_Q_GAL.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
The ratio Q of infrared to radio luminosity of galaxies dominated by star formation is a well-defined and universal quantity (Helou et al. 1985; de Jong et al. 1985). Out of 550 galaxies brighter than 5 Jy at 60um, only two objects, NGC 1377 and IC 1953, are characterized by a ratio Q more than a factor of 10 and more than 6 sigma greater than the average value (Condon et al. 1990). We propose to obtain photometry and spectroscopy with ISO on these two objects to help determine why they are different, and thereby gain more insight into the physics of the basic radio-IR correlation. Using ISO data in combination with ground-based data we hope to discriminate between two hypotheses that might explain this singularly high ratio: (1) an abnormally weak interstellar magnetic field, or (2) that we happen to observe the galaxies at a privileged, very early epoch in a star-formation burst. Hypothesis (1) predicts an interstellar medium dominated by low-density ionized and photo-dissociated regions (PDR), with little mass in the cold, dense molecular phase; hypothesis (2) predicts the reverse. The atomic fine-structure lines accessible to LWS will yield physical parameters (density, pressure, T) for PDRs, while the ionic lines will probe the HII regions. Long-wavelength PHT photometry will yield the dust temperature distribution. These diagnostics will allow us to test the hypotheses above, both directly and by comparison with "normal" star forming galaxies observed under the Guaranteed Time programme.