MASSIVE WARM/HOT GALAXY CORONAE AS PROBED by UV/X-RAY OXYGEN ABSORPTION and EMISSION. I. BASIC MODEL

We construct an analytic phenomenological model for extended warm/hot gaseous coronae of L _∗ galaxies. We consider UV O vi Cosmic Origins Spectrograph (COS)-Halos absorption line data in combination with Milky Way (MW) X-ray O vii and O viii absorption and emission. We fit these data with a single model representing the COS-Halos galaxies and a Galactic corona. Our model is multi-phased, with hot and warm gas components, each with a (turbulent) log-normal distribution of temperatures and densities. The hot gas, traced by the X-ray absorption and emission, is in hydrostatic equilibrium in an MW gravitational potential. The median temperature of the hot gas is 1.5×10⁶K and the mean hydrogen density is ∼5×10^-5 cm^-3. The warm component as traced by the O vi, is gas that has cooled out of the high density tail of the hot component. The total warm/hot gas mass is high and is 1.2×10¹¹M⊙. The gas metallicity we require to reproduce the oxygen ion column densities is 0.5 solar. The warm O vi component has a short cooling time (∼2 ×10⁸years), as hinted by observations. The hot component, however, is ∼ 80%of the total gas mass and is relatively long-lived, with t_cool ∼7 ×10⁹ years. Our model supports suggestions that hot galactic coronae can contain significant amounts of gas. These reservoirs may enable galaxies to continue forming stars steadily for long periods of time and account for "missing baryons" in galaxies in the local universe.