Comparison of models for the warm-hot circumgalactic medium around Milky Way-like galaxies

Abstract

A systematic comparison of the models of the circumgalactic medium (CGM) and their observables is crucial to understanding the predictive power of the models and constraining physical processes that affect the thermodynamics of CGM. This paper compares four analytic CGM models: precipitation, isentropic, cooling flow, and baryon pasting models for the hot, volume-filling CGM phase, all assuming hydrostatic or quasi-hydrostatic equilibrium. We show that for fiducial parameters of the CGM of a Milky Way (MW)-like galaxy (Mvir ∼ 1012 M☉ at z ∼ 0), the thermodynamic profiles – entropy, density, temperature, and pressure – show most significant differences between different models at small (r ≲ 30 kpc) and large scales (r ≳ 100 kpc) while converging at intermediate scales. The slope of the entropy profile, which is one of the most important differentiators between models, is ≈ 0.8 for the precipitation and cooling flow models, while it is ≈ 0.6 and 0 for the baryon pasting and isentropic models, respectively. We make predictions for various observational quantities for an MW mass halo for the different models, including the projected Sunyaev–Zeldovich effect, soft X-ray emission (0.5–2 keV), dispersion measure, and column densities of oxygen ions (O VI, O VII, and O VIII) observable in absorption. We provide Python packages to compute the thermodynamic and observable quantities for the different CGM models. © 2024 The Author(s).