ar X iv : a st ro - p h / 01 04 31 7 v 1 1 9 A pr 2 00 1 The Detection of a Cooling Flow Elliptical Galaxy from O VI Emission

Cooling flow models for the hot gas in elliptical galaxies predict that gas is cooling at a rate of ∼ 1 M⊙ yr , yet there is little evidence for this phenomenon beyond the X-ray waveband. If hot gas is cooling, it will pass through the 3× 10 K regime and radiate in the O VI λλ1032,1038 ultraviolet lines, which can be detected with the Far Ultraviolet Spectroscopic Explorer (FUSE ) and here we report on FUSE observations of the X-ray bright early-type galaxies NGC 1404 and NGC 4636. In NGC 1404, the O VI doublet is not detected, implying a cooling rate < 0.3 M⊙ yr, which is below the predicted values from the cooling flow model of 0.4–0.9 M⊙ yr . In NGC 4636, both O VI lines are clearly detected, indicating a cooling rate of 0.43±0.06 M⊙ yr , which falls within the range of values from the cooling flow prediction, 0.36–2.3 M⊙ yr and is closest to the model where the production of the cooled gas is distributed through the galaxy. The emission line widths, 44±15 km s, are close to the Doppler broadening value (30 km s), indicating that the flow is quiescent rather than turbulent, and that the flow velocity is < 30 km s. Subject headings: galaxies: individual (NGC 1404, NGC 4636) — galaxies: ISM