Virialization of the Inner CGM in the FIRE Simulations and Implications for Galaxy Disks, Star Formation, and Feedback

We use the FIRE-2 cosmological simulations to study formation of a quasi-static, virial-temperature gas phase in circumgalactic medium (CGM) at redshifts 0<z<5, and how this virialized affects evolution galactic discs. demonstrate that when halo mass crosses ~10^12 M_sun, cooling time shocked inner CGM (~0.1 R_vir, where R_vir is virial radius) exceeds local free-fall time. The then experiences transition from on average sub-virial temperatures (T<<T_vir), large pressure fluctuations supersonic inflow/outflow velocities, (T~T_vir), uniform pressures subsonic velocities. This occurs outer (~0.5 R_vir) already has temperature ~T_vir, indicating longer times radii allow virialize lower masses than CGM. outside-in virialization scenario contrast with inside-out scenarios commonly envisioned based more idealized simulations. coincides abrupt changes central galaxy its stellar feedback: settles into stable rotating disc, star transitions `bursty' `steady,' stellar-driven galaxy-scale outflows are suppressed. Our results thus suggest initially associated rotation-dominated thin discs, rather quenching as often assumed.