FAR ULTRAVIOLET SPECTROSCOP1C EXPLORER OBSERVATIONS OF THE GALACTIC AND INTERGALACTIC MEDIUM TOWARD H1821+643

摘要

We have obtained moderate-resolution spectra of the bright QSO H1821+ 643 (z = 0.297) in the wavelength interval 990-1185 A with the Far Ultraviolet Spectroscopic Explorer (FUSE). Strong, complex O Ⅵ λ1032 and Fe Ⅱ λ1145 absorption arising in gas above several spiral arms and the outer warp of our Galaxy is detected. We have identified absorption by a high negative-velocity (-215 km s~(-1)) component of O Ⅵ, which corresponds to the limiting velocity of v_(LSR)～-190 ± 20 km s~(-1) for Milky Way gas along this line of sight, assuming corotation of disk and halo gas and a flat rotation curve for the outer Galaxy. We report the detection of four absorbers in the intergalactic medium, through detections of Lyβ at z = 0.02438 and 0.1213, Lyδ, Lyε, Lyζ in a system at z = 0.2249, C Ⅲ λ977 at z = 0.1705, and O Ⅵ λ1032 at z = 0.12137. The FUSE data show that the Lyman absorbers at z = 0.225 are composed of two components separated by ～70 km s~(-1). Finally, we have observed associated absorption from O Ⅲ λ832, O Ⅳ λ787, and possibly S Ⅴ λ786 at the redshift of the QSO (z ～ 0.297). Ne Ⅷ λλ770, 780 is not detected in this associated system. When combined with the previous detection of associated O Ⅵ λ1032, we conclude that this system is a multiphase absorber, and we discuss the origin of the absorption in this context.