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Introduction

Many Seyfert galaxies show a significant amount of star formation, particularly in their nuclear regions. As long ago as 1984, Telesco et al (1984) showed that half the bolometric luminosity of NGC1068 is produced by star formation activity, and more recently Mouri & Taniguchi (1992) have argued that much of the FIR emission in Seyferts is produced by star formation activity. This raises the question of whether star formation may be a dominant energy source in Seyfert galaxies. Since the bolometric luminosity of most such galaxies is dominated by the far-infrared (FIR) luminosity, we may use the radio- FIR correlation to examine this hypothesis. Normal spiral and starburst galaxies show a tight correlation between their radio and FIR luminosity (e.g. Wunderlich et al., 1987). This correlation, which extends over five orders of magnitude, is true for both flux density and luminosity, and cannot be accounted for by selection effects, or a simple “richness effect”. While a detailed mechanism to explain this correlation has yet to be established, it is almost certainly the result of star formation, which generates both the synchrotron radio emission and the thermal FIR emission. This is supported by the fact that all objects that are dominated by star formation (HII galaxies, normal spirals, starburst galaxies) do follow the correlation.

On the other hand, Sopp & Alexander (1991) showed that radio-loud quasars and radio galaxies clearly do not follow the radio-far-infrared correlation. Thus whether or not a galaxy follows this correlation may be used as an indicator of the dominant energy source of the galaxy. For example, Roy & Norris (1996) cross-correlated the PMN 6-cm survey with the IRAS point-source catalogue and found a number of objects deviating from the radio-FIR correlation. Most Seyfert and starburst galaxies generally followed the correlation, whilst those departing from it included BL Lac objects and radio galaxies.