Highly Ionized High‐Velocity Clouds: Intergalactic Gas in the Local Group or Distant Gas in the Galactic Halo?

Abstract

In the course of our studies of the gaseous halo surrounding the Milky Way, we have recently identified several high-velocity clouds (HVCs; V_LSR -1 are favored if the clouds are located in the distant Galactic halo since the cloud sizes scale inversely with metallicity. We provide a summary of the HVCs detected in absorption at intermediate resolution with the GHRS and the IUE satellite and find that C IV HVCs are detected along three of 10 extragalactic sight lines down to a level of logN(C iv)~13.3 (3 sigma).