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J.N. Bregman, E.D. Miller, J.A. Irwin (University of Michigan)
The cooling flow rate in the X-ray luminous ellipticals is estimated at about 1 Msolar yr-1 from the X-ray data . The cooled gas is not detected as HI or molecular material nor is it consumed in normal star formation, and the lack of these components has raised doubt about the cooling flow model. If the gas actually cools at the X-ray rate, it passes through the 3x105 K region and produces OVI emission, which can be detected with the Far Ultraviolet Spectroscopic Explorer (FUSE). Here we report on FUSE observations for two classic cooling flow galaxies, NGC 1404 and NGC 4636. In NGC 4636, we detect the OVI doublet at a luminosity that implies a cooling rate of 0.3 Msolar yr-1. The FUSE aperture encloses about 1/7 of the total X-ray emission and the observed cooling rate is about 1/7 of the total inferred from the X-rays, providing a strong confirmation of the cooling flow model. However, there is surprising variation between galaxies, because in NGC 1404, we obtain only an upper limit for OVI emission, implying a cooling rate at least five times below the value predicted from the X-ray data. We would like to acknowledge support from NASA and assistance from the FUSE instrument team.
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