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.
Instrument
CAM01 , LWS02
Temporal Coverage
1998-02-05T00:46:47Z/1998-02-12T01:07:19Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, Helou et al., 1999, 'EXCEPTIONS TO THE RADIO-INFRARED CORRELATION: RADIO-DEFICIENT GALAXIES', 1.0, European Space Agency, https://doi.org/10.5270/esa-w3q3ior
