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

Stern, Jonathan and Faucher-Giguère, Claude-André and Fielding, Drummond and Quataert, Eliot and Hafen, Zachary and Gurvich, Alexander B. and Ma, Xiangcheng and Byrne, Lindsey and El-Badry, Kareem and Anglés-Alcázar, Daniel and Chan, T. K. and Feldmann, Robert and Kereš, Dušan and Wetzel, Andrew and Murray, Norman and Hopkins, Philip F. (2021) 'Virialization of the Inner CGM in the FIRE Simulations and Implications for Galaxy Disks, Star Formation, and Feedback.', The Astrophysical Journal, 911 (2). p. 88.


We use the FIRE-2 cosmological simulations to study the formation of a quasi-static, virial-temperature gas phase in the circumgalactic medium (CGM) at redshifts 0 < z < 5 and how the formation of this virialized phase affects the evolution of galactic disks. We demonstrate that when the halo mass crosses ∼1012 M⊙, the cooling time of shocked gas in the inner CGM (∼0.1Rvir, where Rvir is the virial radius) exceeds the local free-fall time. The inner CGM then experiences a transition from on average subvirial temperatures (T ≪ Tvir), large pressure fluctuations, and supersonic inflow/outflow velocities to virial temperatures (T ∼ Tvir), uniform pressures, and subsonic velocities. This transition occurs when the outer CGM (∼0.5Rvir) is already subsonic and has a temperature ∼Tvir, indicating that the longer cooling times at large radii allow the outer CGM to virialize at lower halo masses than the inner CGM. This outside-in CGM virialization scenario is in contrast with inside-out scenarios commonly envisioned based on more idealized simulations. We demonstrate that inner CGM virialization coincides with abrupt changes in the central galaxy and its stellar feedback: the galaxy settles into a stable rotating disk, star formation transitions from "bursty" to "steady," and stellar-driven galaxy-scale outflows are suppressed. Our results thus suggest that CGM virialization is initially associated with the formation of rotation-dominated thin galactic disks, rather than with the quenching of star formation as often assumed.

Item Type:Article
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Publisher statement:© 2021. The American Astronomical Society. All rights reserved.
Date accepted:28 December 2020
Date deposited:11 January 2022
Date of first online publication:19 April 2021
Date first made open access:11 January 2022

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