Excitation mechanism of forbidden Fe II 1.644 micron emission in Seyfert and starburst galaxies

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view Abstract Citations (48) References (65) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Excitation Mechanism of Fe II 1.644 Micron Emission in Seyfert and Starburst Galaxies Mouri, Hideaki ; Nishida, Minoru ; Taniguchi, Yoshiaki ; Kawara, Kimiaki Abstract To study the excitation mechanism of near-infrared [Fe II] (a^4^ F_9/2_-a^4^D_7/2_) emission at 1.644 microns in Seyfert and starburst galaxies, we compare the intensity of [Fe II] 1.644 micron with those of optical lines, [O I] λ6300, [S II] (λ6717 + λ6731), and [N II] λ6584, and we find a good correlation between the line ratio of [Fe II] 1.644 microns to hydrogen Brγ ([Fe II]/Brγ) and that of [O I] λ6300 to Hα ([O I]/Hα). No correlation between (Fe II]/Brγ and [N II]/Hα is found. The [O I] line is radiated from partly ionized hydrogen regions (hydrogen transition regions), while the [N II] line is radiated from fully ionized regions. Thus, it is concluded that the [Fe II] emission comes mainly from the transition regions in galactic nuclei and is excited by electron collisions. The observed correlation between [Fe II]/Brγ and [O I]/Hα can be explained by assuming that the [Fe II] and [O I] lines are radiated from the spatially similar regions. The [Fe II]/Brγ ratio is higher in active galactic nuclei (AGNs) than in starburst nuclei (SBNs). This property can be interpreted as being due to the presence of extended transition regions outside the fully ionized hydrogen zone in AGNs. The broad line widths of [Fe II] emission of NGC 1068 and NGC 4151 suggest that the [Fe II] emission comes from the narrow-line regions (NLRs). If this is the case, heating of gas due to nonthermal radiation plays an important role in the excitation of the [Fe II] emission in AGNs. On the other hand, in SBNs, the [Fe II] emission may not be due to photoionization by young OB stars but may be due to shock beating caused by starburst winds. Publication: The Astrophysical Journal Pub Date: September 1990 DOI: 10.1086/169095 Bibcode: 1990ApJ...360...55M Keywords: Forbidden Transitions; Infrared Radiation; Metallicity; Seyfert Galaxies; Starburst Galaxies; Astronomical Spectroscopy; Iron; Line Spectra; Nitrogen; Astrophysics; GALAXIES: NUCLEI; GALAXIES: SEYFERT; INFRARED: SPECTRA; LINE FORMATION full text sources ADS | data products SIMBAD (22) NED (20)

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