The Nucleus of the Seyfert Galaxy NGC 4151
1968; IOP Publishing; Volume: 151; Linguagem: Inglês
10.1086/149486
ISSN1538-4357
Autores Tópico(s)Astrophysics and Star Formation Studies
Resumoview Abstract Citations (216) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Nucleus of the Seyfert Galaxy NGC 4151 Oke, J. B. ; Sargent, Wallace L. W. Abstract We have studied the optical and near-infrared spectrum of the nucleus of NGC 4151. The observations consist of photographic spectrograms covering the wavelength range XX3500-6800 and photoelectric measurements of the continuous energy distribution and emission-line strengths in the range XX3300- 11000. We infer that the emission lines arise in at least two physically distinct regions. First there is a region, having N6 `S-' 5000 cm3, Te "s-' 200000 K, and a mass of about 2 X 1O~ Mo, which gives rise to the main emission-line spectrum. This component fills only about 4~i~ of the total volume of the nucleus, 50 Pc 111 diameter, and appears to be in the form of clouds or filaments in relative motion with velocities of about 450 km/sec. This gas is probably ionized and heated by degradation of the mass motions. It is likely that the difference in line profile between permitted and forbidden lines is due to electron scattering. Second, there is a region which gives rise to coronal lines of [Fe x] and [Fe xiv] discovered by 0. C. Wilson. The temperature of this gas is about 106 ° K, but Ne cannot be determined directly from the spectrum However, the adopted value of N. = 100 cm3 would both fill the whole volume of the nucleus and also keep this hot gas in pressure equilibrium with the cool clouds. The mass of the coronal gas is «= 1O~ Mo The recombination radiation from these two regions cannot account for the observed optical con- tinuum. There are no stellar absorption features in the continuous spectrum of the nucleus which must, therefore, be partly non-thermal. NGC 4151 is only a weak radio source, and we consider ways of pro~ ducing a non-thermal optical continuum while suppressing radio-frequency synchrotron radiation Free- free absorption and possibly the Tsytovich effect appear able to attenuate radio frequencies below a few GHz. We estimate that energy must be continuously supplied to generate the mass motions in the nucleus, rather than a single explosive event Publication: The Astrophysical Journal Pub Date: March 1968 DOI: 10.1086/149486 Bibcode: 1968ApJ...151..807O full text sources ADS | data products NED (1)
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