Abstract
We describe the detection of neutral gas within the central galaxy of the Centaurus cluster of galaxies, NGC 4696. The detection is in the form of sodium D absorption, against the background stellar emission. The gas is clearly associated with the compact emission filament system and dust lane in the central 20'' of the galaxy; it shares the same velocity field as the emission-line gas, the absorption line strength correlates with the amount of extinction due to dust, and the equivalent width of narrow absorption features is related to the emission-line strength. The quantitative relationship between absorption line strength and extinction is compared with Galactic ratios. The strength of sodium absorption is large for the typical E(B-V) observed, although similar to what is found in external spiral galaxies. Several possibilities may account for this, including larger internal random motions than are present in the Galactic ISM, higher gas-to-dust ratio than Galactic, or a higher neutral fraction of sodium in NGC 4696. The observations imply a common origin for the warm and neutral components, which may be a merger.
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