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Date and Time of the Query: 2019-08-18 T07:08:25 PDT
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For refcode 2005ApJ...635.1031B:
Retrieve 24 NED objects in this reference.
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Copyright by American Astronomical Society. Reproduced by permission
2005ApJ...635.1031B O VI in Elliptical Galaxies: Indicators of Cooling Flows Joel N. Bregman, Eric D. Miller, Alex E. Athey, and Jimmy A. Irwin Abstract. Early-type galaxies often contain a hot X-ray -- emitting interstellar medium [(3 -- 8)x10^6^ K] with an apparent radiative cooling time much less than a Hubble time. If unopposed by a heating mechanism, the gas will radiatively cool to temperatures <~10^4^ K at a rate proportional to L_X_/T_X_, typically 0.03 -- 1 M_sun_ yr^-1^. We can test whether gas is cooling through the 3x10^5^ K range by observing the O VI doublet, whose luminosity is proportional to the cooling rate. Here we report on a study of an unbiased sample of 24 galaxies, obtaining Far Ultraviolet Spectroscopic Explorer spectra to complement the X-ray data of ROSAT and Chandra. The O VI line emission was detected in about 40% of the galaxies and at a luminosity level similar to the prediction from the cooling flow model. There is a correlation between M^dot^_OVI_ and M^dot^_X_, although there is significant dispersion about the relationship, where the O VI is brighter or dimmer than expected by a factor of 3 or more. If the cooling flow picture is to be retained, then this dispersion requires that cooling flows be time-dependent, as might occur by the activity of an AGN. However, of detected objects, those with the highest or lowest values of M^dot^_OVI_/M^dot^_X_ are not systematically hot or cool, as one might predict from AGN heating. Key words: Galaxies: Cooling Flows, Galaxies: ISM, Ultraviolet: Galaxies, X-Rays: Galaxies
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