Thermal Instability in the CGM of $L_{\star}$ Galaxies: Testing 'Precipitation' Models with the FIRE Simulations
| Autor: | Zachary Hafen, Claude André Faucher-Giguère, Andrew Wetzel, Eliot Quataert, Clarke J. Esmerian, Andrey V. Kravtsov, Dušan Kereš, Jonathan Stern |
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| Rok vydání: | 2020 |
| Předmět: |
Physics
Number density Thermodynamic state 010308 nuclear & particles physics Metallicity FOS: Physical sciences Astronomy and Astrophysics Astrophysics Radius Astrophysics::Cosmology and Extragalactic Astrophysics 01 natural sciences Astrophysics - Astrophysics of Galaxies Galaxy law.invention 13. Climate action Space and Planetary Science law Astrophysics of Galaxies (astro-ph.GA) 0103 physical sciences Satellite galaxy Galaxy formation and evolution Hydrostatic equilibrium 010303 astronomy & astrophysics Astrophysics::Galaxy Astrophysics |
| DOI: | 10.48550/arxiv.2006.13945 |
| Popis: | We examine the thermodynamic state and cooling of the low-$z$ Circum-Galactic Medium (CGM) in five FIRE-2 galaxy formation simulations of Milky Way-mass galaxies. We find that the CGM in these simulations is generally multiphase and dynamic, with a wide spectrum of largely nonlinear density perturbations sourced by the accretion of gas from the Inter-Galactic Medium (IGM) and outflows from both the central and satellite galaxies. We investigate the origin of the multiphase structure of the CGM with a particle tracking analysis and find that most of the low entropy gas has cooled from the hot halo as a result of thermal instability triggered by these perturbations. The ratio of cooling to free-fall timescales $t_{\rm cool}/t_{\rm ff}$ in the hot component of the CGM spans a wide range $\sim 1-100$ at a given radius, but exhibits approximately constant median values $\sim 5-20$ at all radii $0.1 R_{\rm vir} < r < R_{\rm vir}$. These are similar to the $\approx 10-20$ value typically adopted as the thermal instability threshold in ``precipitation'' models of the ICM. Consequently, a one-dimensional model based on the assumption of a constant $t_{\rm cool}/t_{\rm ff}$ and hydrostatic equilibrium approximately reproduces the number density and entropy profiles of each simulation, but only if it assumes the metallicity profile and temperature boundary condition taken directly from the simulation. We explicitly show that the $t_{\rm cool}/t_{\rm ff}$ value of a gas parcel in the hot component of the CGM does not predict its probability of subsequently accreting onto the central galaxy. This suggests that the value of $t_{\rm cool}/t_{\rm ff}$ is a poor predictor of thermal stability in gaseous halos in which large-amplitude density perturbations are prevalent. Updated to match published version. Note: a bug was found in the code used to create Figure 8 - corrected version strengthens conclusions of paper, which remain unchanged |
| Databáze: | OpenAIRE |
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