The High-velocity Gas toward Messier 5: Tracing Feedback Flows in the Inner Galaxy

We present FUSE and STIS E140M observations of the post-AGB star ZNG 1 in the globular cluster Messier 5 (l 1⁄4 3:9", b 1⁄4þ47:7"; d 1⁄4 7:5 kpc, z 1⁄4þ5:3 kpc). High-velocity absorption is seen in C iv, Si iv, O vi, and lower ionization species at LSR velocities of roughly$140 and$110 km s$1.We conclude that this gas is not circumstellar on the basis of photoionization models and path length arguments. Thus, the high-velocity gas along the ZNG 1 sight line is the first evidence that highly ionized HVCs can be found near the Galactic disk. We measure the metallicity of these HVCs to be 1⁄2O/H&1⁄4 þ0:22' 0:10, the highest of any known HVC. Given the clouds’ metallicity and distance constraints, we conclude that these HVCs have a Galactic origin. This sight line probes gas toward the inner Galaxy, and we discuss the possibility that these HVCs may be related to a Galactic nuclear wind or Galactic fountain circulation in the inner regions of the Milky Way. Subject headinggs: ISM: abundances — ISM: clouds — ISM: structure — stars: individual (NGC 5904 ZNG 1) — ultraviolet: ISM