Far Infrared Observations of Radio Quasars and FR II Radio Galaxies

We report MIPS photometry of 20 radio-loud quasars and galaxies at 24 and 70 um (and of five at 160 um). We combine this sample with additional sources detected in the far infrared by IRAS and ISO for a total of 47 objects, including 23 steep spectrum Type I AGNs: radio-loud quasars and broad line radio galaxies; and 24 Type II AGNs: narrow line and weak line FR II radio galaxies. Of this sample, the far infrared emission of all but 3C 380 appears to be dominated by emission by dust heated by the AGN and by star formation. The AGN appears to contribute more than 50% of the far infrared luminosity in most of sources. It is also expected that the material around the nucleus is optically thin in the far infrared. Thus, the measurements at these wavelengths can be used to test the orientation-dependent unification model. As predicted by the model, the behavior of the sources is consistent with the presence of an obscuring circumnuclear torus; in fact, we find it may still have significant optical depth at 24 um.In addition, as expected for the radio-loud quasars, there is a significant correlation between the low frequency radio (178 MHz) and the 70 um emission, two presumably isotropic indicators of nuclear activity. This result is consistent with the simple unified scheme. However, there is a population of radio galaxies that are underluminous at 70 um compared with the radio-loud quasars and hence are a challenge to the simple unified model.