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Date and Time of the Query: 2019-06-19 T10:50:00 PDT
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For refcode 1997ApJ...482..747A:
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Copyright by American Astronomical Society. Reproduced by permission
1997ApJ...482..747A Using Near-Infrared [Fe II] Lines to Identify Active Galaxies ALMUDENA ALONSO-HERRERO, M. J. RIEKE, G. H. RIEKE, AND M. RUIZ Steward Observatory, University of Arizona, Tucson, AZ 85721 Received 1996 September 30; accepted 1997 January 15 ABSTRACT The ([Fe II] 1.644 micron)/Br{gamma} and ([Fe II] 1.2567micron)/Pa{beta} ratios provide good separation of starburst and Seyfert galaxies; we show that ([Fe II] 1.644 micron)/Br{gamma} is nearly as good a discriminant as the commonly used ([O I] {lambda}6300)/H{alpha} ratio.The behavior of both the ([O I] {lambda}6300)/H{alpha} and the ([Fe II] 1.644 micron)/Br{gamma} ratios is readily understood if there is a progression in the proportion of shock excitation going from H II region through starburst and Seyfert galaxies to supernova remnants. We use the CLOUDY program to show that the behavior is also explained if the dominant excitation mechanism is photoionization. As a test of this technique for identifying excitation mechanisms, we have obtained infrared spectra of two LINER galaxies. NGC 1052, which is thought to be excited by a nuclear power-law UV source, is the prototype of LINERs, and NGC 3504 is classified as a weak-[O I] {lambda}6300 LINER, better understood in terms of photoionization by O stars than by a nonstellar source. The placement of these galaxies on the ([Fe II] 1.644 micron)/Br{gamma} versus ([O I] {lambda}6300)/H{alpha} diagram is in agreement with these previously determined characteristics. The ([Fe II] 1.644 micron)/Br{gamma} and ([Fe II] 1.2567 micron)/Pa{beta} ratios should be useful in classifying heavily obscured galaxies because the ratios (1) are constructed at wavelengths where extinction is relatively small and (2) involve lines over narrow spectral ranges. Subject headings: galaxies: fundamental parameters-galaxies: individual (NGC 1052, NGC 3504)-galaxies: Seyfert-galaxies: starburst-infrared: galaxies
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