2001/04/19 by Joel N. Bregman, Eric D. Miller, Jimmy A. Irwin
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1086/320675
to be published in ApJ Letters; 8 Latex pages with 2 embedded figures
arxiv created 2001/04/19 · openalex publication_date 2001/06/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
Cooling flow models for the hot gas in elliptical galaxies predict that gas is cooling at a rate of ~1 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 × 10 5 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 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 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 .