A pair of OVI and broad Ly α absorbers probing warm gas in a galaxy group environment at z ∼ 0.4☆

We report the detection of two O VI absorbers at z=0.416 14 and 0.419 50 (|Delta v| = 710 km s(-1)), 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. OVI has a velocity structure different from other metal species. Ly alpha shows the presence of a broad feature. The linewidths for OVI and the broad Ly alpha suggest T = 7.1 x 10(5) 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 HI and OVI. Here a temperature of 4.6 x 10(4) K supports OVI originating in a low- density photoionized gas. A broad component is seen in Ly alpha, offset from OVI. The temperature in the broad Ly alpha is T less than or similar to 2.1 x 10(5) K. The absorbers reside in a galaxy overdensity region with seven spectroscopically identified galaxies within similar to 10 Mpc and Delta v similar to 1000 km s(-1) 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.