O VI Absorbers Tracing Hot Gas Associated with a Pair of Galaxies at z = 0.167

High signal-to-noise observations of the QSO PKS 0405-123 (z(em) = 0.572) with the Cosmic Origins Spectrograph from 1134 to 1796 angstrom with a resolution of similar to 17 km s(-1) are used to study the multi-phase partial Lyman limit system (LLS) at z = 0.16716, which has previously been studied using relatively low signal-to-noise spectra from STIS and FUSE. The LLS and an associated HI-free broad OVI absorber likely originate in the circumgalactic gas associated with a pair of galaxies at z = 0.1688 and 0.1670 with impact parameters of 116 h(70)(-1) and 99 h(70)(-1). The broad and symmetric OVI absorption is detected in the z = 0.16716 rest frame with v = -278 +/- 3 km s(-1), logN(OVI) = 13.90 +/- 0.03, and b = 52 +/- 2 km s(-1). This absorber is not detected in HI or other species with the possible exception of NV. The broad, symmetric OVI profile and the absence of corresponding HI absorption indicate that the circumgalactic gas in which the collisionally ionized OVI arises is hot (log T similar to 5.8-6.2). The absorber may represent a rare but important new class of low-z intergalactic medium absorbers. The LLS has strong asymmetrical OVI absorption with logN(OVI) = 14.72 +/- 0.02 spanning a velocity range from -200 to + 100 km s(-1). The high and low ions in the LLS have properties resembling those found for Galactic highly ionized high-velocity clouds where the OVI is likely produced in the conductive and turbulent interfaces between cool and hot gas.