Ultra-strong Mg ii absorbers as a signature of cool intragroup gas

We present the results of a spectroscopic survey of galaxies in the vicinity of an ultra-strong MgII ⋋⋋2786, 2803 absorber of rest-frame absorption equivalent width ᵣ (2796) = 4. 2Å at z = 0. 5624. This absorber was originally found at projected separation p = 246 kpc of a luminous red galaxy (LRG) at z = 0. 5604. Magellan IMACs spectroscopy has revealed two galaxies at p 1 Gyr) and little on-going star formation activity (SFR 3. 0 M_☉/yr. Including the two ultra-strong MgII absorbers analyzed by Nestor et al. (2011), this is the third ultra-strong absorber for which a detailed study of the galactic environment is available. All three aborbers are found in galaxy groups. We examine different physical mechanisms rise to the absorbing gas including starburst driven-outflows, cold filaments, extended rotating disks, and stripped gas. We argue that the large equivalent width in these absorbers is more likely due to the gas dynamics of the intragroup medium rather than driven by starburst outflows.