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We survey the highly ionized circumgalactic media (CGM) of 29 blindlyselected galaxies at 0.49 < z_(gal) < 1.44 based on high-S/N ultravioletspectra of z > 1 QSOs and the galaxy database from the COS Absorption Survey ofBaryon Harbors (CASBaH). We detect the Ne VIII doublet in nine of the galaxies,and for gas with N(Ne VIII) > 10^13.3 cm^-2 (> 10^13.5 cm^-2), we derive a NeVIII covering fraction f_c = 75 +15/-25% (44 +22/-20%) within impact parameter(rho) < 200 kpc of M_* = 10^(9.5-11.5) Msol galaxies and f_c = 70 +16/-22% (f_c= 42 +20/-17%) within rho < 1.5 virial radii. We estimate the mass in NeVIII-traced gas to be M_gas(Ne VIII) > 10^9.5 Msol (Z/Zsol)^-1, or 6-20% of theexpected baryonic mass if the Ne VIII absorbers have solar metallicity.Ionizing Ne VII to Ne VIII requires 207 eV, and photons with this energy arescarce in the CGM. However, for the median halo mass and redshift of oursample, the virial temperature is close to the peak temperature for the Ne VIIIion, and the Ne VIII-bearing gas is plausibly collisionally ionized near thistemperature. Moreover, we find that photoionized Ne VIII requires cool andlow-density clouds that would be highly underpressured (by approximately twoorders of magnitude) relative to the putative, ambient virialized medium,complicating scenarios where such clouds could survive. Thus, more complex(e.g., non-equilibrium) models may be required; this first statistical sampleof Ne VIII absorber/galaxy systems will provide stringent constraints forfuture CGM studies.

The COS Absorption Survey of Baryon Harbors (CASBaH): Warm-hot Circumgalactic Gas Reservoirs Traced by Ne VIII Absorption