Giant lobes of plasma extend 55 degrees above and below the Galactic Center, glowing in emission from gamma rays (the Fermi Bubbles) to microwaves (the WMAP haze) and polarized radio waves. We use ultraviolet absorption-line spectra from the Hubble S
pace Telescope to constrain the velocity of the outflowing gas within these regions, targeting the quasar PDS 456 (Galactic coordinates l,b=10.4, +11.2 degrees). This sightline passes through a clear biconical structure seen in hard X-ray and gamma-ray emission near the base of the northern Fermi Bubble. We report two high-velocity metal absorption components, at v_LSR=-235 and +250 km/s, which cannot be explained by co-rotating gas in the Galactic disk or halo. Their velocities are suggestive of an origin on the front and back side of an expanding biconical outflow emanating from the Galactic Center. We develop simple kinematic biconical outflow models that can explain these observed profiles with an outflow velocity of ~900 km/s and a full opening angle of ~110 degrees (matching the X-ray bicone). This indicates Galactic Center activity over the last ~2.5-4.0 Myr, in line with age estimates of the Fermi Bubbles. The observations illustrate the use of UV absorption-line spectroscopy to probe the properties of swept-up gas venting into the Fermi Bubbles.
We present a detection of a broad Ly-alpha absorber (BLA) with a matching O VI line in the nearby universe. The BLA is detected at z = 0.01028 in the high S/N spectrum of Mrk 290 obtained using the Cosmic Origins Spectrograph. The Ly-alpha absorption
has two components, with b(HI) = 55 +/- 1 km/s and b(HI) = 33 +/- 1 km/s, separated in velocity by v ~ 115 km/s. The O VI, detected by FUSE at z = 0.01027, has a b(OVI) = 29 +/- 3 km/s and is kinematically well aligned with the broader HI component. The different line widths of the BLA and OVI suggest a temperature of T = 1.4 x 10^5 K in the absorber. The observed line strength ratios and line widths favor an ionization scenario in which both ion-electron collisions and UV photons contribute to the ionization in the gas. Such a model requires a low-metallicity of -1.7 dex, ionization parameter of log U ~ -1.4, a large total hydrogen column density of N(H) ~ 4 x 10^19 cm^-2, and a path length of 400 kpc. The line of sight to Mrk 290 intercepts at the redshift of the absorber, a megaparsec scale filamentary structure extending over 20 deg in the sky, with several luminous galaxies distributed within 1.5 Mpc projected distance from the absorber. The collisionally ionized gas in this absorber is likely tracing a shock-heated gaseous structure, consistent with a few different scenarios for the origin, including an over-dense region of the WHIM in the galaxy filament or highly ionized gas in the extended halo of one of the galaxies in the filament. In general, BLAs with metals provide an efficient means to study T ~ 10^5 - 10^6 K gas in galaxy halos and in the intergalactic medium. A substantial fraction of the baryons missing from the present universe is predicted to be in such environments in the form of highly ionized plasma.
We report on the detection of Ne VIII in an intervening multiphase absorption line system at z=0.32566 in the FUSE spectrum of the quasar 3C 263. The Ne VIII 770 A line detection has a 3.9 sigma significance. At the same velocity we also find absorpt
ion lines from C IV, O III, O IV and N IV. The line parameter measurements yield log [N(Ne VIII), cm^-2] =13.98 (+0.10,-0.13) and b = 49.8 +/- 5.5 km/s. We find that the ionization mechanism in the gas phase giving rise to the Ne VIII absorption is inconsistent with photoionization. The absorber has a multi-phase structure, with the intermediate ions produced in cool photoionized gas and the Ne VIII most likely in a warm collisionally ionized medium in the temperature range (0.5 - 1.0) x 10^6 K. This is the second ever detection of an intervening Ne VIII absorption system. Its properties resemble the previous Ne VIII absorber reported by Savage et al. (2005). Direct observations of H I and O VI are needed to better constrain the physical conditions in the collisionally ionized gas phase of this absorber.
