2016MNRAS.458..733P

We report the detection of two O vi absorbers at z=0.416 14 and 0.419 50 (|Δv|=710 km/s), towards SBS 0957+599. Both absorbers are multiphase systems tracing substantial reservoirs of warm baryons. The low- and intermediate-ionization metals in the z=0.416 14 absorber are consistent with an origin in photoionized gas. O vi has a velocity structure different from other metal species. Ly α shows the presence of a broad feature. The linewidths for O vi and the broad Ly α suggest T=7.1 x 10⁵ K. This warm medium is probing a baryonic column, which is an order of magnitude more than the total hydrogen in the cooler photoionized gas. The second absorber is detected only in H i and O vi. Here a temperature of 4.6 x 10⁴ K supports O vi originating in a low-density photoionized gas. A broad component is seen in Ly α, offset from O vi. The temperature in the broad Ly α is T <= 2.1 x 10⁵ K. The absorbers reside in a galaxy overdensity region with seven spectroscopically identified galaxies within ∼10 Mpc and Δv ∼ 1000 km/s of the z=0.416 14 absorber, and two galaxies inside a similar separation from the z=0.419 50 absorber. The distribution of galaxies relative to the absorbers suggests that the line of sight could be intercepting a large-scale filament connecting galaxy groups, or the extended halo of a sub-L* galaxy. Though kinematically proximate, the two absorbers reaffirm the diversity in the physical conditions of low red-shift O vi systems and the galactic environments they inhabit.