QSOs - some studies are no more luminous than Markarian...

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QSOs : It was hard enough to tell that they were in galaxies, much less surrounded by others. Imaging from Mauna Kea has been extremely suggestive, with Hutchings and Campbell 1983 (Nature 303, 984) claiming that 30% of QSOs with z < 0.6 show evidence of interactions. Spectroscopy by Stockton (1979 IAU Symp. 92, 89) and Heckman et al. (1984 AJ 89, 958) confirms the association of these galaxies in redshift, and Stockton 1982 (ApJ 257, 33) has shown that many of the companions have their own low-luminosity active nuclei. Further individual systems have been studied by, for example, Shara et al 1985 (ApJ 246, 339; 4C 18.68), Yee and Green 1987 (AJ 94, 618; PG 1613+658), and Vader et al 1987 (AJ 94, 847; IRAS 00275-2359). Be careful in putting the statistical studies together; many of the "QSOs" in
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Unformatted text preview: some studies are no more luminous than Markarian Seyferts, so that it is not clear which problem is being addressed. Calling the Sun a quasar doesn't answer the quasar-physics problem. Anyway, as was long expected, HST results have added considerably to our understanding. Most QSO host galaxies have compact companions within tens of kpc (Bahcall et al. 1995 ApJ 450, 486, Disney et al. 1995 Nature 376, 150), a result which was foreshadowed by Stockton's 1982 paper. This fraction is by now the most striking correlation of nuclear activity and galaxy interactions. Some of these companions are seen in this montage of HST images, from rather luminous normal companions to the very close, compact companions of PKS 1302-102 and PKS 2349-013....
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