Far Ultraviolet Spectroscopic Explorer observations of the galactic and intergalactic medium toward H1821+643

We have obtained moderate-resolution spectra of the bright QSO H1821+643 (z = 0.297) in the wavelength interval 990-1185 Angstrom with the Far Ultravi olet Spectroscopic Explorer (FUSE). Strong, complex O VI lambda 1032 and Fe II lambda 1145 absorption arising in gas above several spiral arms and the outer warp of our Galaxy is detected. We have identified absorption by a h igh negative-velocity (-215 km s(-1)) component of O VI, which corresponds to the limiting velocity of v(LSR) similar to -190 +/- 20 km s(-1) for Milk y Way gas along this line of sight, assuming corotation of disk and halo ga s and a flat rotation curve for the outer Galaxy. We report the detection o f four absorbers in the intergalactic medium, through detections of Ly beta at z = 0.02438 and 0.1213, Ly delta, Ly epsilon, Ly zeta in a system at z = 2249, C III lambda 977 at z = 0.1705, and O VI lambda 1032 at z = 0.12137 . The FUSE data show that the Lyman absorbers at z = 0.225 are composed of two components separated by similar to 70 km s(-1). Finally, we have observ ed associated absorption from O III lambda 832, O IV lambda 787, and possib ly S v lambda 786 at the redshift of the QSO (z similar to 0.297). Ne VIII lambda lambda 770, 780 is not detected in this associated system. When comb ined with the previous detection of associated O VI lambda 1032, we conclud e that this system is a multiphase absorber, and we discuss the origin of t he absorption in this context.