The Broad‐Line and Narrow‐Line Regions of the LINER NGC 4579

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Abstract
We report the discovery of an extremely broad Hα 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 Hα line of FWHM ≈ 2300 km s-1 and FWZI ≈ 5000 km s-1. New spectra obtained with the Hubble Space Telescope (HST) and a 02 wide slit reveal an Hα component with an FWZI of ~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 Hα 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] λλ6716, 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.
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