The Physics of Extragalactic Gas: One Argument for a Next Generation   Space Telescope
  Observations of the Galactic ISM have had tremendous impact on our understanding of the physics of galactic gas and the processes of galaxy formation. Similar observations at z>2 reveal the neutral baryonic content of the universe, trace the evolution of metal enrichment, shed light on process of nucleosynthesis and dust formation, and yield precise measurements of galactic velocity fields. Owing to the limitations of UV spectroscopy, however, researchers are unable to examine galactic gas at 0<z<2, an epoch spanning ~80% of the current universe. To complement the multitude of ongoing programs to identify and research z<2 galaxies, a next generation space telescope is essential to investigate the gas which feeds and records the history of galaxy formation. 
Jason X. Prochaska (UCO/Lick Observatory)