tokens: ; Grimes et al. 2009 ; Tripp et al. 2011 ; Tumlinson et al. 2011 ; Muzahid 2014 ). This is not the case for either of our O vi absorbers. The sub-solar metallicity, which we obtain for the low- and high-ionization gas phases, is also not usually found in metal-rich outflows (Muzahid 2014 ). Thus, there is no definitive evidence for the absorbers discussed in this paper being directly associated with a galactic-scale wind. These warm absorbers may be tracers of ancient outflows (wind age >1 Gyr), which, as the simulations of Ford et al. ( 2014 ) suggest, can end up diffusely distributed at galactocentric distances of d ≳ 500 kpc where absorption from the ambient intergalactic medium also dominates. With the limited SDSS sampling of galaxies discussed in this paper, it is difficult to distinguish an outflow-generated O vi from the several other possible scenarios that can give rise to warm O vi in galaxy haloes (see Heckman et al. 2002 ; Sembach et al. 2003 ; Maller Bullock 2004 ; Tripp et al. 2008 ). Based on models of structure formation, it has been hypothesized that galaxy groups can have intragroup gas at T ∼ 10 5 –10 6 K, temperatures too low to discriminate their emission from the soft X-ray background (Mulchaey et al. 1996 ). Presently, such a medium can be probed only through high-ionization absorption lines such as O vi , Ne viii and thermally broadened Ly α against the light from background QSOs. Exploring this gas reservoir is important, as it potentially harbours as much as ∼4 per cent of the total baryons in the low- z Universe, on a par with the fraction of baryons trapped inside galaxies (Savage et al. 2014 ). A recent example is given by Stocke et al. ( 2014 ), whose sample of BLA–O vi warm absorbers is more likely to be from intragroup gas than individual galaxy haloes. The warm O vi is hypothesized to arise in conductive interface layers between cold T ≲ 3 × 10 4 K clouds and a hitherto undetected diffuse T ∼ 10 6.5 K intragroup medium. Hydrodynamic simulations also predict that a substantial fraction of baryons are to be found along large-scale filaments connecting galaxy overdensity regions. In Narayanan et al. ( 2011 ), a BLA–O vi absorber is identified as tracing T ∼ 1.4 × 10 5 K intergalactic gas along a nearby galaxy filament ( v HELIO = 3081 km s −1 ), with several loose groups of galaxies beyond ρ ∼ 1.5 Mpc of projected separation. Another example of baryonic reservoirs along galaxy filaments is given by Wakker et al. ( 2015 ). About 85 per cent of the Ly α systems from their sample of 15 absorbers, which includes BLAs, appear to be tracing intergalactic filament gas that lies far outside the virial radii of the nearest galaxies that trace the filament. Along similar lines, Tejos et al. ( 2016 ) found a ∼4–7 times higher covering fraction for BLAs near galaxy overdensities, compared to random fields. In that study also, the warm gas was identified as being away from individual galaxy haloes, but possibly along cluster
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