The 1200-3200 A spectra of Seyfert I galaxies : MK 304, NGC 7603, MCG8-11-11, ESO 12-G 21 and NGC 1566.

Abstract

The 5 Seyfert I galaxies MK 304, NGC 7603, MCG 8-11-11, ESO 12-G 21, and NGC 1566 have been observed with IUE (1200 - 3200 Å). Their UV spectrum is rich in emission lines. A steep rise of the continuum toward shorter wavelengths is observed below ≡2000 Å in 4 of these objects; this excess is interpreted as thermal emission from an accretion disk. For a sample of 23 Seyfert galaxies, a significant inverse correlation is found between the strength of the Fe II optical lines - relative to that of H_β - vs. the C IV 1550/C III] 1908 intensity ratio. The intensities of the emission lines correlate with that of the continuum, supporting thus photoionization models of the broad line region (BLR). The authors postulate that most of the missing emission arises through collisional excitation in a high density/opacity zone of the BLR. Collisional model calculations are carried out that include the hydrogen, Fe II, Mg II, C II 1335, and C II] 2325 lines.