NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-07-23 T20:11:33 PDT
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For refcode 2017ApJ...846..102M:
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2017ApJ...846..102M Emission Line Properties of Seyfert Galaxies in the 12 micron Sample Malkan, Matthew A.; Jensen, Lisbeth D.; Rodriguez, David R.; Spinoglio, Luigi; Rush, Brian Abstract. We present optical and ultraviolet spectroscopic measurements of the emission lines of 81 Seyfert 1 and 104 Seyfert 2 galaxies that comprise nearly all of the IRAS 12 micron AGN sample. We have analyzed the emission-line luminosity functions, reddening, and other diagnostics. For example, the narrow-line regions (NLR) of Seyfert 1 and 2 galaxies do not significantly differ from each other in most of these diagnostics. Combining the Halpha/Hbeta ratio with a new reddening indicator---the [S II]6720/[O II]3727 ratio---we find the average E(B-V) is 0.49 +/- 0.35 for type 1 and 0.52 +/- 0.26 for type 2 Seyferts. The NLR of Sy1s has an ionization level insignificantly higher than that of Sy2s. For the broad-line region (BLR), we find that the C IV equivalent width correlates more strongly with [O III]/Hbeta than with UV luminosity. Our bright sample of local active galaxies includes 22 Seyfert nuclei with extremely weak broad wings in Halpha, known as Seyfert 1.9s and 1.8s, depending on whether or not broad Hbeta wings are detected. Aside from these weak broad lines, our low-luminosity Seyferts are more similar to the Sy2s than to Sy1s. In a BPT diagram, we find that Sy1.8s and 1.9s overlap the region occupied by Sy2s. We compare our results on optical emission lines with those obtained by previous investigators, using AGN subsamples from the Sloan Digital Sky Survey. The luminosity functions of forbidden emission lines [O II]lambda3727 A, [O III]lambda5007 A, and [S II]lambda6720 A in Sy1s and Sy 2s are indistinguishable. They all show strong downward curvature. Unlike the LFs of Seyfert galaxies measured by the Sloan Digital Sky Survey, ours are nearly flat at low luminosities. The larger number of faint Sloan "AGN" is attributable to their inclusion of weakly emitting LINERs and H II+AGN "composite" nuclei, which do not meet our spectral classification criteria for Seyferts. In an Appendix, we have investigated which emission line luminosities can provide the most reliable measures of the total non-stellar luminosity, estimated from our extensive multi-wavelength database. The hard X-ray or near-ultraviolet continuum luminosity can be crudely predicted from either the [O III]lambda5007 A luminosity or the combinations of [O III]+Hbeta or [N II]+Halpha lines, with a scatter of +/- 4 times for Sy1s and +/- 10 times for Sy2s. Although these uncertainties are large, the latter two hybrid (NLR+BLR) indicators have the advantage of predicting the same HX luminosity independent of Seyfert type. Key words: galaxies: active, galaxies: luminosity function, mass function, galaxies: nuclei, galaxies: Seyfert, infrared: galaxies, quasars: emission lines
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