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C. M. Urry (Yale University)
According to the unification paradigm, active galaxies present a vastly different appearance depending on their orientation to the line of sight. Both relativistic beaming of the jet emission and obscuration of the central continuum and broad-line emission are important. Unification explains most observations of active galaxy spectra and number counts, once the strong selection effects are taken into account. There are still some puzzling issues, such as whether the unification model continues to hold in the early Universe, where active galaxies are most numerous. New multiwavelength surveys like GOODS will answer this question. Meanwhile, the ubiquity of supermassive black holes in local galaxies, and the correlation between their mass and the stellar dynamics, suggest a need for ``Grand Unification'' between active and normal galaxies. It seems increasingly likely that the process of bulge formation in young galaxies is tied closely to the growth of the central black hole and to the epoch of peak activity in galaxy nuclei.
This work has been supported by NASA.
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.