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The circumgalactic medium (CGM) is closely linked to galaxy formation and evolution, but difficult to characterize observationally and typically poorly resolved in cosmological simulations. We use spherically-symmetric, idealized, high-resolution simulations of the CGM in $10^{12}M_\odot$ and $10^{11}M_\odot$ dark matter halos to characterize the gas pressure, turbulent and radial velocities, and degree of thermal and effective dynamic pressure support in the overall CGM as well as in its high- and low-temperature phases. We find that the $10^{12}M_\odot$ halo contains a CGM mostly formed of a hot gas halo in hydrostatic equilibrium out of which cold gas condenses and falls onto the central galaxy, while the $10^{11}M_\odot$ halo's CGM is not in hydrostatic equilibrium, has a wider spread of properties at a given galactocentric radius, does not have a clear separation of hot and cold phases, and is dominated by bulk motions. We also find that the degree of pressure support in the $10^{11}M_\odot$ halo is strongly dependent on the parameters of the galactic winds of the central galaxy. These results promote the idea that there is no "average" CGM and care must be taken when setting the initial conditions for a small-box simulation of a patch of the CGM., 20 pages, 17 figures, accepted by MNRAS

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., Comment: 28 pages, 13 figures, accepted to MNRAS