The detection of a cooling flow elliptical galaxy from OVI emission

Cooling flow models for the hot gas in elliptical galaxies predict that gas is cooling at a rate of similar to1 M-. yr(-1), yet there is little evidence for this phenomenon beyond the X-ray wave band. If hot gas is cooling, it will pass through the 3 x 10(5) K regime and radiate in the O VI lambda lambda 1032, 1038 ultraviolet lines, which can be detected with the Far-Ultraviolet Spectroscopic Explorer (FUSE), and here we report on FUSE observations of the Xray bright early-type galaxies NGC 1404 and NGC 4636. In NGC 1404, the O vi doublet is not detected, implying a cooling rate less than 0.3 M-. yr(-1), which is below the predicted values from the cooling flow model of 0.4-0.9 M-. yr(-1). In NGC 4636, both O VI lines are clearly detected, indicating a cooling rate of 0.43 +/- 0.06 M-. yr(-1), which falls within the range of values from the cooling flow prediction, 0.36-2.3 M-. yr(-1), and is closest to the M model where the production of the cooled gas is distributed through the galaxy. The emission-line widths, 44 +/- 15 km s(-1), are close to the Doppler broadening value (30 km s(-1)), indicating that the flow is quiescent rather than turbulent and that the flow velocity is less than 30 km s(-1).