Direct images and spatially resolved spectra have been obtained for five QSOs having a wide range of radio, optical, and X-ray luminosity. The two lowest luminosity objects clearly show absorption features identified with stars in a host galaxy at the QSO redshift. Such features are possibly seen in two others but not in the highest luminosity object, in which nebulosity is barely discernable. All objects show off-nuclear changes in continuum color and in emission-line intensities and ratios. The radio-loud objects have more luminous host galaxies, strong and extended forbidden O II and forbidden O III, and UV-bright nuclei. They tend to have optically luminous nuclei, high nuclear to galaxy luminosity ratios, and blue host galaxies.
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Hickson et al. (1987) studied this question.
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