scientific abstract several arguments from radio astronomy suggest that all radio-loud qsos are beamed towards us (barthel 1989, apj 336, 606) and that these quasars should be identified with favourably oriented luminous radio galaxies such as cygnus-a (e.g., djorgovski et al. 1991, apj 372, l67, and vestergaard & barthel 1993, aj 105, 456). as part of our multispectral project to investigate this unification model (e.g., hes et al. 1993, nature 326, 362) we wish to carry out far-infrared photometry on (radio luminosity) matched samples of intermediate redshift quasars and radio galaxies from the 3c-catalog. testing the unified scheme at far-ir wavelengths will be crucial. this spectral band is believed to sample thermal (re)radiation from dust surrounding the active nucleus (e.g., sanders et al. 1989, apj 347, 29), which is emitted isotropically. the far-ir properties of qsr and prgs in our matched samples should therefore be the same. attempts based on the iras database have yielded ambiguous results, due to the limited sensitivity (e.g. heckman et al. 1992, apj 391, 39). moderate differences in far-ir luminosities -- if present -- may moreover be explained with wavelength dependent aspect effects (pier & krolik 1993, apj 401, 99). we therefore wish to carry out this test using isophot, observing at 60, 90 and 170 micron and at 25 micron. with the additional observation at 25 micron we might be able to disentangle contributions from hot, inner dust and cool outer dust. combining the fir with optical data we will be able to separate out additional effects from dust associated with starforming regions. observation summary the objects are generally known to be fainter than 100 mjy at 60 micron. some limits for the radio galaxies are below 40 mjy at 60 micron. we expect the objects to become brighter with increasing wavelength. all of the objects will be observed with isophot in mode pht22 with the c200 and the c10...0 detectors in a sequence with filters 160, 90 and 60 micron. integration times will be 128 secs per filter, bringing the total time per object to 641 secs. the 25 micron observations will be carried out as well, with pht03 and filter #12 at 25 micron and detector p2. integration times will be 128 seconds per object, summing up to a total of 805 seconds per object, including overhead. this will lead to a 5 sigma detection of about 7 mjy at 60 and 90 micron and 20 mjy at 160 and 25 micron. these sensitivities should be sufficient to detect all the objects.
The Infrared Space Observatory (ISO) was the world's 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.