The Puzzle of LINERs and the Warm Ionized Gas in Early-type Galaxies

Ever since their discovery, the nature of low ionization nuclear emission-line regions (LINERs) has been hotly debated. Some authors treat them as AGNs,others argue they are not AGNs but powered by shocks or hot old stars.No universal agreement has been reached. On the other hand, early-type galaxies frequently contain spatially extended warm ionized gas and have spectra similar to LINERs. How is this large-scale emission related to the nuclear LINERs? Because LINER is the most common spectral type found in massive galaxies in both nuclear and integrated spectra, understanding its nature is important to numerous topics in astrophysics.

In this talk, you will hear a story of how I converted from a supporter for AGN-powering of LINER line emission to an opponent, and what kind of convincing evidence made me convert. I will also discuss what we can learn about the warm ionized gas in early-type galaxies from this line emission, given that it is not an AGN indicator.