The Shocking Power Sources of LINERs
Nearly half of all nearby galaxies are low-ionization nuclear emission-line regions (LINERs), the majority of which harbor supermassive black holes with very low accretion rates. However the accretion flows are not energetic enough to power the emission observed within the central 100 pc, requiring additional power sources that are unresolved on these scales. I will present spectra of three nearby luminous LINERs with ten times higher spatial resolution. All three objects have multiple indicators of an accreting black hole, as well as a deficient energy budget. I will discuss the measured diagnostic emission line ratios as a function of distance from the nucleus, and how they compare to theoretical models for different excitation mechanisms commonly invoked to describe LINER emission. The physical model that best describes these galaxies comprises a low-luminosity, accretion-powered active nucleus that photoionizes the gas close in to the galaxy center, and shocks that excite the gas at larger distances. Therefore, the characteristic LINER spectrum observed within the central 100 pc may be the result of multiple physical mechanisms at work on smaller spatial scales.