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E.M. Murphy (U. Virginia), B. Otte, J.C. Howk (JHU), Q.D. Wang (U. Massachusetts), W.R. Oegerle (NASA/GSFC), K.R. Sembach (STScI), FUSE Science Team
Observations with the Far Ultraviolet Spectroscopic Explorer have revealed the presence of emission from O VI ions in the hot halo of the edge-on spiral galaxy NGC 4631. To our knowledge, this is the first detection of O VI in emission in a spiral galaxy other than the Milky Way. We believe that this detection is the best evidence yet for a "galactic fountain" operating in a spiral galaxy. In a galactic fountain, hot gas from multiple, overlapping supernovae rises into the halo of a galaxy, cools, and falls back to the disk (Shapiro and Field, 1976, ApJ, 205, 762). As the galactic fountain gas cools through a temperature of 300,000 K it will emit strong O VI lines.
Emission from O VI was detected in two positions north and east of the nucleus of NGC 4631. The upper position is on the peak of the soft (0.13-0.3 kev) X-ray emission detected by Wang et al. (1995, ApJ, 439, 176) using ROSAT and the lower position is between a series of H-alpha features that have been identified as possible superbubbles and chimneys by Wang et al. (2001, ApJ, 555, L99). The detection of O VI in emission allows us to estimate the total mass flux and luminosity of the cooling gas assuming that the O VI has the same distribution as the soft X-ray emission seen by ROSAT and Chandra. In addition, we compute these same quantities assuming that the O VI halo covers the entire galaxy. We compare these results to the estimated mechanical power input by supernovae. Cycle 3 FUSE observations will allow us to better constrain the total cooling luminosity by determining the extent of the O VI halo.
This work is supported by NASA contract NAS5-32985 to the Johns Hopkins University.
The author(s) of this abstract have provided an email address for comments about the abstract: emm8x@virginia.edu