NEAR-INFRARED EMISSION-LINE SPECTRA OF THE ORION NEBULA, NGC-4151, AND OTHER SEYFERT-GALAXIES

Near-infrared CCD spectra, covering the wavelength interval of approximately λλ7000-11000 at moderate resolution (FWHM ≈ 6 Å), were obtained of NGC 1976 and NGC 4151 in three overlapping segments. The wavelengths and relative line fluxes were measured, and most of the lines were identified. The strongest three lines in both objects are, in order, [S III] λ9531, He I λ10830, and [S III] λ9069. The Orion Nebula spectrum is very helpful for identifying lines in NGC 4151 and for comparison with it. Among the ions identified in NGC 1976, many of them previously known, are [Fe II], [Ni II], [Ni II], [Cl II], and [C I]. Likewise, in NGC 4151, [C I], [Fe II], [Fe XI], [Cl II], [Ni II], [Ar III], [Ar V], and [S II] are all present, and probably [S VIII] as well, in addition to H I, He I, and He II. Lower resolution (FWHM ≈ 12 Å) spectra covering the range λλ7000-10000 of 14 additional Seyfert galaxies were also obtained and measured. The strongest line in all but two of them is [S III] λ9531. Nearly all these galaxies show the strongest [Ni II] line, λ7378. Comparison of line strengths among these various Seyfert galaxies allow the ionization behavior to be traced. One unidentified line, λ7865, that is present in the spectra of NGC 4151, III Zw 77, and three other galaxies, is probably a high-ionization forbidden line. Two other unidentified emission lines apparently observed in two or more Seyfert galaxies are λ9138 and λ9191. The best additional diagnostic information the near-infrared spectral region provides, the [S III] (λ9069 + λ9531)/λ6312 ratio, is not as useful as the analogous [O III] ratio, due to the blending of λ6312 and the greater wavelength interval of the [S III] ratio.