Massive Warm/Hot Galaxy Coronae. II. Isentropic Model

Abstract

Abstract We construct a new analytic phenomenological model for the extended circumgalactic material (CGM) of L* galaxies. Our model reproduces the O vii/O viii absorption observations of the Milky Way (MW) and the O vi measurements reported by the COS-Halos and eCGM surveys. The warm/hot gas is in hydrostatic equilibrium in an MW gravitational potential, and we adopt a barotropic equation of state, resulting in a temperature variation as a function of radius. A pressure component with an adiabatic index of is included to approximate the effects of a magnetic field and cosmic rays. We introduce a metallicity gradient motivated by the enrichment of the inner CGM by the Galaxy. We then present our fiducial model for the corona, tuned to reproduce the observed O vi–O viii column densities and with a total mass of inside . The gas densities in the CGM are low ( cm−3), and its collisional ionization state is modified by the metagalactic radiation field. We show that for O vi-bearing warm/hot gas with typical observed column densities cm−2 at large ( kpc) impact parameters from the central galaxies, the ratio of the cooling to dynamical times, / , has a model-independent upper limit of . In our model, / at large radii is . We present predictions for a wide range of future observations of the warm/hot CGM, from UV/X-ray absorption and emission spectroscopy to dispersion measure and Sunyaev–Zel’dovich cosmic microwave background measurements. We provide the model outputs in machine-readable data files for easy comparison and analysis.