Does the Milky Way Produce a Nuclear Galactic Wind?

We detect high-velocity absorbing gas using Hubble Space Telescope and FarUltraviolet Spectroscopic Explorer medium resolution spectroscopy along twohigh-latitude AGN sight lines (Mrk 1383 and PKS 2005-489) above and below theGalactic Center (GC). These absorptions are most straightforwardly interpretedas a wind emanating from the GC which does not escape from the Galaxy'sgravitational potential. Spectra of four comparison B stars are used toidentify and remove foreground velocity components from the absorption-lineprofiles of O VI, N V, C II, C III, C IV, Si II, Si III, and Si IV. Twohigh-velocity (HV) absorption components are detected along each AGN sightline, three redshifted and one blueshifted. Assuming that the four HV featurestrace a large-scale Galactic wind emanating from the GC, the blueshiftedabsorber is falling toward the GC at a velocity of 250 +/- 20 km/s, which canbe explained by "Galactic fountain" material that originated in a boundGalactic wind. The other three absorbers represent outflowing material; thelargest derived outflow velocity is +250 +/- 20 km/s, which is only 45% of thevelocity necessary for the absorber to escape from its current position in theGalactic gravitational potential. All four HV absorbers are found to reach thesame maximum height above the Galactic plane (|z_max| = 12 +/- 1 kpc), implyingthat they were all ejected from the GC with the same initial velocity. Thederived metallicity limits of >10-20% Solar are lower than expected formaterial recently ejected from the GC unless these absorbers also containsignificant amounts of hotter gas in unseen ionization stages.Comment: 39 pages, 3 figures, ApJ accepte