AAS 197, January 2001
Session 3. QSO Absorbers and the IGM
Display, Monday, January 8, 2001, 9:30am-7:00pm, Exhibit Hall

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[3.17] FUSE Observations of Intergalactic and Interstellar Gas Toward 3C 273

K.R. Sembach, J.C. Howk, W.R. Oegerle (JHU), B.D. Savage (U. Wisconsin), J.M. Shull, M. Giroux (U. Colorado), FUSE Science Team

We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the intergalactic and interstellar absorption along the sight line toward the bright QSO 3C 273 (z = 0.1583). The FUSE data have a spectral resolution of 20 km~s-1 and cover the 905-1187 Å\ wavelength region. The spectrum contains signatures of cold molecular gas (H2), warm atomic and ionized gas (\ion{H}{1}, \ion{C}{2}, \ion{C}{3}, \ion{N}{1}, \ion{N}{2}, \ion{O}{1}, \ion{P}{2}, \ion{S}{3}, \ion{Ar}{1}, \ion{Fe}{2}, \ion{Fe}{3}), and hot collisionally-ionized gas (\ion{O}{6}).

The 3C 273 sight line samples intergalactic gas, including gas in the Virgo Cluster. We clearly detect Ly\beta absorption in the z = 0.0033, 0.0053, 0.0294, 0.1201, and 0.1466 absorbers identified through previous Ly\alpha investigations at longer wavelengths. Weak Ly\beta lines may be present for several other known absorbers along the sight line. We also detect higher order \ion{H}{1} Lyman series lines in the stronger Virgo absorber (z = 0.0053). We tentatively identify \ion{O}{6} and \ion{C}{3} absorption associated with the z = 0.1201 system. We will comment on the significance of these measurements and their implications for understanding the \ion{H}{1} and hot gas content of the absorbers.

Within the Milky Way, the 3C 273 sight line passes through an X-ray enhancement in the North Polar Spur near the edge of the Radio Loops I and IV. This region is part of a large interstellar structure created by multiple supernova explosions that have vented energy from the disk into the halo. Very strong \ion{O}{6} absorption is associated with this gas; we find log N(\ion{O}{6}) = 14.72±.03, which is the largest column density of \ion{O}{6} yet observed for any sight line though the Galactic halo. We will comment briefly on the origin of this \ion{O}{6} absorption and its relationship to other ionized species observed by FUSE.

FUSE is a NASA Origins mission operated by the Johns Hopkins University. Funding for this work is provided through NASA contract NAS-532985.

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