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The nucleus of a galaxy that shows a characteristic emission-line spectrum; it is an acronym for low-ionization nuclear emission region. A liner's spectrum is dominated by emission lines from low ionization states (e.g. O II, N II, S II), with only weak emission lines from higher ionization states (e.g. O III, Ne III, He II). The spectrum is evidence of unusual activity in the nucleus, probably not associated with normal stars, and may result from the heating of interstellar matter, either by radiation from a central source or by shock waves generated by supernova explosions. The linewidths are similar to those seen in Seyfert galaxies and, like Seyferts, the activity seems to occur more often in S0, Sa, and Sb galaxies than in other types.

Subjects: Astronomy and Astrophysics.

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