Ultraviolet Quasar Absorption Line Spectroscopy of z ∼ 1 Galaxy Group

We used ultraviolet spectra from HST/STIS (R = 30, 000), together with optical spectra from Keck/HIRES (R = 45, 000), to study the three MgII-selected absorption systems at z = 0.9254, 0.9276, and 0.9342 toward the quasar PG 1206 + 459. A multi-phase gaseous structure, with low-ionization components produced in small condensations and high-ionization ones in diffuse clouds, is indicated in all three systems. Each system is likely to represent a different galaxy with absorption due to some combination of interstellar medium, coronal gas, halo gas, and high-velocity clouds. Even with the improved sensitivity of HST/COS, we will only be able to obtain high-resolution ultraviolet spectra of the brightest quasars in the sky. A larger telescope with ultraviolet coverage will enable quasar absorption line studies of hundreds of galaxies, including a wide range of galaxy types and environments at low and intermediate redshifts.