A panoramic view of the circumgalactic medium in the photoionized
  precipitation model
  We consider a model of the circumgalactic medium (CGM) in which feedback
maintains a constant ratio of cooling time to freefall time throughout the
halo, so that the entire CGM is marginally unstable to multiphase condensation.
This 'precipitation model' is motivated by observations of multiphase gas in
the cores of galaxy clusters and the halos of massive ellipticals. We derive
from the model density and temperature profiles for the CGM around galaxies
with masses similar to the Milky Way. After taking into consideration the
geometrical position of our solar system in the Milky Way, we show that the CGM
model is consistent with observed OVI, OVII, and OVIII column densities only if
temperature fluctuations with a log-normal dispersion $\sigma_{\ln T} \sim
0.6$-$1.0$ are included. We show that OVI column densities observed around
star-forming galaxies require systematically greater values of $\sigma_{\ln T}$
than around passive galaxies, implying a connection between star formation in
the disk and the state of the CGM. Photoionization by an extra-galactic UV
background does not significantly change these CGM features for galaxies like
the Milky Way but has much greater and significant effects on the CGM of
lower-mass galaxies.
