AAS 203rd Meeting, January 2004
Session 41 Warm-Hot IM
Poster, Tuesday, January 6, 2004, 9:20am-6:30pm, Grand Hall

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[41.02] Highly Ionized Gas in the Galactic Halo and the High Velocity Clouds Toward PG 1116+215

R. Ganguly, K. R. Sembach (STScI), T. M. Tripp (U. Massachusetts - Amherst), B. D. Savage (U. Wisconsin - Madison)

Recent observations of extragalactic objects with FUSE have revealed the presence of high ionization OVI absorption associated with high velocity clouds (HVCs), defined as gas which lies at absolute velocities beyond 100 km/s in the Local Standard of Rest. We have acquired high spectral resolution observations with STIS (~ 10 km/s) and FUSE (~ 20 km/s) of the quasar PG 1116+215. The spectra show absorption at Vlsr=184km/s from a wide range of ionization species:CIV, OI, OVI, MgII, SiII, SiIII, SiIV, and FeII. The strong and broad O VI absorption in this HVC extends from ~ 120 to 230 km/s with a weak wing of absorption to 300km/s. Although the HVC is not seen in HI 21 cm emission down to N(HI)~ 2x1018 cm-2, it is seen in the HI Lyman series up to at least the 918.13Åline. In addition, we have non-detection constraints on the column denisties of CI, NI, NV, and SII. We can rule out photoionization in an ultra-low density (n~ 10-6 cm-3) Local Group medium adopted by some investigators to explain the O VI and O VII absorption detected in several directions. We are currently in the process of determining if these data either support or rule out other models of HVCs, such as the Warm-Hot Intergalactic Medium, Dark Matter dominated mini-halos, or interactions with a low density (10-4-10-5 cm-3) Galactic corona or Local Group medium. In addition, we will also use abundance infomation to study the enrichment history and constrain possible sources for the high velocity gas, such as tidal debris from cannibalized galaxies.

The author(s) of this abstract have provided an email address for comments about the abstract: ganguly@stsci.edu

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