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 theLINER nucleus of NGC 4579. From ground-based observations, the galaxy waspreviously known to contain a Type 1 nucleus with a broad H-alpha line of FWHM= 2300 km/s and FWZI ~ 5000 km/s. New spectra obtained with the Hubble SpaceTelescope and a 0.2 arcsec-wide slit reveal an H-alpha component with FWZI ~18,000 km/s. The line is not obviously double-peaked, but it does possessshoulders on the red and blue sides which resemble the H-alpha profiles ofdouble-peaked emitters such as NGC 4203 and NGC 4450. This similarity suggeststhat the very broad H-alpha profile in NGC 4579 may represent emission from anaccretion disk. Three such objects have been found recently in two HST programswhich have targeted a total of 30 galaxies, demonstrating that double-peaked orextremely broad-line emission in LINERs must be much more common than would beinferred from ground-based surveys. The ratio of the narrow [S II] 6716, 6731lines shows a pronounced gradient indicating a steep rise in density toward thenucleus. The direct detection of a density gradient within the inner arcsecondof the narrow-line region confirms expectations from previous observations oflinewidth-critical density correlations in several LINERs.Comment: 8 pages, includes 3 figures. To appear in The Astrophysical Journa