The formation and physical origin of highly ionized cooling gas
  We present a simple model that explains the origin of warm diffuse gas seen
primarily as highly ionized absorption line systems in the spectra of
background sources. We predict the observed column densities of several highly
ionized transitions such as OVI, OVIII, NeVIII, NV, and MgX; and present a
unified comparison of the model predictions with absorption lines seen in the
Milky Way disk, Milky Way halo,starburst galaxies, the circumgalactic medium
and the intergalactic medium at low and high redshifts. We show that diffuse
gas seen in such diverse environments can be simultaneously explained by a
simple model of radiatively cooling gas. We show that most of such absorption
line systems are consistent with being collisionally ionized, and estimate the
maximum likelihood temperature of the gas in each observation. This model
satisfactorily explains why OVI is regularly observed around star-forming low-z
L* galaxies, and why NV is rarely seen around the same galaxies. We further
present some consequences of this model in quantifying the dynamics of the
cooling gas around galaxies and predict the shock velocities associated with
such flows. A unique strength of this model is that while it has only one free
(but physically well-constrained) parameter, it nevertheless successfully
reproduces the available data on O VI absorbers in the interstellar,
circumgalactic, intra-group, and intergalactic media, as well as the available
data on other absorption-line from highly ionized species.
