Fast Winds Drive Slow Shells: A Model for the Circumgalactic Medium as
  Galactic Wind-Driven Bubbles
  Successful models of the low redshift circumgalactic medium (CGM) must
account for (1) a large amount of gas, (2) relatively slow gas velocities, (3)
a high degree of metal enrichment, (4) the similar absorption properties around
both star-forming and passive galaxies, and (5) the observationally inferred
temperature and densities of the CGM gas. We show that galactic wind-driven
bubbles can account for these observed properties. We develop a model
describing the motion of bubbles driven by a hot, fast galactic wind
characteristic of supernova energy injection. The bubble size grows slowly to
hundreds of kiloparsecs over $5-10$ Gyr. For high star formation rates or high
wind mass loading $\dot M_w/\dot M_\star$, the free-flowing hot wind, the
shocked hot wind in the interior of the bubble, and the swept-up halo gas
within the bubble shell can all radiatively cool and contribute to
low-ionization state metal line absorption. We verify that if the free-flowing
wind cools, the shocked wind does as well. We find effective mass loading
factors of $(M_w+M_\mathrm{swept})/M_\star\sim5-12$ as the bubbles sweep into
the CGM. We predict cool gas masses, velocities, column densities, metal
content, and absorption line velocities and linewidths of the bubble for a
range of parameter choices. This picture can reproduce many of the COS-Halos
and Keeney et al. (2017) observations of low-ionization state metal absorption
lines around both star-forming and passive galaxies.
