Figuring Out Gas & Galaxies in Enzo (FOGGIE). VI. The Circumgalactic Medium of L^* Galaxies Is Supported in an Emergent, Nonhydrostatic Equilibrium

Journal Article · 04 May 2023 · The Astrophysical Journal

DOI: https://doi.org/10.3847/1538-4357/acbb06 · OSTI ID:1974435

Lochhaas, Cassandra  ^[1]; Tumlinson, Jason  ^[2]; Peeples, Molly S.  ^[2]; O’Shea, Brian W.  ^[3]; Werk, Jessica K.  ^[4]; Simons, Raymond C.  ^[5]; Juno, James  ^[6]; Kopenhafer, Claire  ^[7]; Augustin, Ramona  ^[1]; Wright, Anna C.  ^[8]; Acharyya, Ayan  ^[8]; Smith, Britton D.  ^[9]

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1. Space Telescope Science Institute, Baltimore, MD (United States)
2. Space Telescope Science Institute, Baltimore, MD (United States); Johns Hopkins Univ., Baltimore, MD (United States)
3. Michigan State Univ., East Lansing, MI (United States). National Superconducting Cyclotron Lab.
4. Univ. of Washington, Seattle, WA (United States)
5. Space Telescope Science Institute, Baltimore, MD (United States); Univ. of Connecticut, Storrs, CT (United States)
6. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
7. Michigan State Univ., East Lansing, MI (United States)
8. Johns Hopkins Univ., Baltimore, MD (United States)
9. Univ. of Edinburgh, Scotland (United Kingdom). The Royal Observatory

The circumgalactic medium (CGM) is often assumed to exist in or near hydrostatic equilibrium, with the regulation of accretion and the effects of feedback treated as perturbations to a stable balance between gravity and thermal pressure. We investigate global hydrostatic equilibrium in the CGM using four highly resolved L* galaxies from the Figuring Out Gas & Galaxies in Enzo (FOGGIE) project. The FOGGIE simulations were specifically targeted at fine spatial and mass resolution in the CGM (Δx ≲ 1 kpc h^–1 and M ≃ 200M_⊙). We develop a new analysis framework that calculates the forces provided by thermal pressure gradients, turbulent pressure gradients, ram pressure gradients of large-scale radial bulk flows, centrifugal rotation, and gravity acting on the gas in the CGM. Thermal and turbulent pressure gradients vary strongly on scales of ≲5 kpc throughout the CGM. Thermal pressure gradients provide the main supporting force only beyond ~0.25R₂₀₀, or ~50 kpc at z = 0. Within ~0.25R₂₀₀, turbulent pressure gradients and rotational support provide stronger forces than thermal pressure. More generally, we find that global equilibrium models are neither appropriate nor predictive for the small scales probed by absorption line observations of the CGM. Local conditions generally cannot be derived by assuming a global equilibrium, but an emergent global equilibrium balancing radially inward and outward forces is obtained when averaging over the nonequilibrium local conditions on large scales in space and time. Approximate hydrostatic equilibrium holds only at large distances from galaxies, even when averaging out small-scale variations.

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: Hubble Space Telescope Archival Research Theory Grant; National Aeronautics and Space Administration (NASA); National Science Foundation (NSF); USDOE Laboratory Directed Research and Development (LDRD) Program
• Grant/Contract Number: AC02-09CH11466; HST AR #16140; 80NSSC18K1105; AST 1812521; NSF-CAREER 2044303; 1908109; 2106575; NNX15AP39G; NSF-AST 1910414; HST AR #15012; NAS 5-26555; ACI-1238993; ACI-1514580
• OSTI ID: 1974435
• Journal Information: The Astrophysical Journal, Vol. 948, Issue 1; ISSN 0004-637X
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: United States
• Language: English