The broad-line and narrow-line regions of the liner NGC 4579

We report the discovery of an extremely broad H alpha emission line in the LINER nucleus of NGC 4579. From ground-based observations, the galaxy was previously known to contain a type 1 nucleus with a broad H alpha line of FWHM approximate to 2300 km s(-1) and FWZI approximate to 5000 km s(-1). New spectra obtained with the Hubble Space Telescope (HST) and a 0.2" wide slit reveal an H alpha component with an FWZI of similar to 18,000 km s(-1). The line is not obviously double peaked, but it does possess "shoulders" on the red and blue sides which resemble the profiles seen in double-peaked emitters such as NGC 4203 and NGC 4450. This similarity suggests that the very broad H alpha profile in NGC 4579 may represent emission from an accretion disk. Three such objects have been found recently in two HST programs which have targeted a total of 30 galaxies, demonstrating that double-peaked or extremely broad-line emission in LINERs must be much more common than would be inferred from ground-based surveys. The ratio of the narrow [S II] lambda lambda 6716, 6731 lines shows a pronounced gradient indicating a steep rise in density toward the nucleus. The direct detection of a density gradient within the inner arcsecond of the narrow-line region confirms expectations from previous observations of line width-critical density correlations in several LINERs.