Accepted 2006 July 20. Received 2006 July 18; in original form 2006 May 26 | Lisa J. Kewley, Brent Groves, Guinevere Kauffmann and Tim Heckman
The paper presents an analysis of 85,224 emission-line galaxies from the Sloan Digital Sky Survey (SDSS) to develop a new empirical classification scheme for Seyfert galaxies, LINERs, and composite objects. The authors show that Seyferts and LINERs form distinct branches on standard optical diagnostic diagrams. They derive a new classification scheme that separates star-forming galaxies, composite active galactic nucleus-H ii (AGN-H ii) galaxies, Seyferts, and LINERs. LINERs are found to be older, more massive, less dusty, less concentrated, have higher velocity dispersions, and lower [O iii] luminosities compared to Seyfert galaxies. The study also investigates the host galaxy properties of these different classes of objects, finding that the majority of LINERs are AGN and that the Seyfert/LINER dichotomy is analogous to high/low-state models. The results suggest that pure LINERs require a harder ionizing radiation field with a lower ionization parameter than Seyfert galaxies, consistent with low and high X-ray binary states.The paper presents an analysis of 85,224 emission-line galaxies from the Sloan Digital Sky Survey (SDSS) to develop a new empirical classification scheme for Seyfert galaxies, LINERs, and composite objects. The authors show that Seyferts and LINERs form distinct branches on standard optical diagnostic diagrams. They derive a new classification scheme that separates star-forming galaxies, composite active galactic nucleus-H ii (AGN-H ii) galaxies, Seyferts, and LINERs. LINERs are found to be older, more massive, less dusty, less concentrated, have higher velocity dispersions, and lower [O iii] luminosities compared to Seyfert galaxies. The study also investigates the host galaxy properties of these different classes of objects, finding that the majority of LINERs are AGN and that the Seyfert/LINER dichotomy is analogous to high/low-state models. The results suggest that pure LINERs require a harder ionizing radiation field with a lower ionization parameter than Seyfert galaxies, consistent with low and high X-ray binary states.