From Observations to Physical Parameters

Accretion/Ejection Phenomena and Emission-Line Profile (A)symmetries in Type-1 Active Galactic Nuclei

“…Perhaps surprisingly, this hypothesis has not gained wide acceptance, even if several lines of evidence are in its favor, as summarized below. (One reason could be that the idea is perceived as "heretic" due to the early attempts to explain the cosmological redshift as gravitational (see the discussion in [50] and Chapter 2 or [51] for historical reports); a second reason is the customary attribution of wavelength shifts to the Doppler effect due to the gas motions. There are alternative processes as shifts due to electron scattering have been proposed [52] but have never been considered for general validity.)…”

The Correlation Luminosity-Velocity Dispersion of Galaxies and Active Galactic Nuclei

“…The consensus that the broadening of emission lines in quasar and Seyfert nuclei results from the Doppler effect, attributed to the rapid motion of the line-emitting gas, emerged early on; already Carl Seyfert, in his initial systematic study of galaxies named after him [11], attributed the large widths of lines to Doppler shifts, with velocities reaching up to approximately 8500 km/s for the hydrogen lines of NGC 3516 and 7469 [12]. The nature of the motions has been debated ever since (see, e.g., and references therein, [13][14][15][16]). The realization that two systems of emission lines-one dominated by virial broadening and one affected by strong outflow motions-are coexisting in AGN came slowly [17][18][19][20][21].…”