Galactic coronae in the intracluster environment: semiconfined stellar-feedback-driven outflows




Recently X-ray observations have shown the regular presence of compact galactic coronae around intermediate-mass spheroid galaxies embedded in the intracluster/intragroup medium (ICM). We conduct 2D hydrodynamic simulations to study the quasi-steady-state properties of such coronae as the natural products of the ongoing distributed stellar feedback semiconfined by the thermal and ram pressures of the ICM. We find that the temperature of a simulated corona depends primarily on the specific energy of the feedback, consistent with the lack of correlation between the observed hot gas temperature and K-band luminosity of galaxies. The simulated coronae typically represent subsonic outflows, chiefly because of the semiconfinement. As a result, the hot gas density increases with the ICM thermal pressure. The ram pressure, on the other hand, mainly affects the size and lopsidedness of the coronae. The density increase could lead to the compression of cool gas clouds, if present, and hence the formation of stars. The increase also enhances radiative cooling of the hot gas, which may fuel central supermassive black holes, explaining the reason that the frequency of active galactic nuclei observed in clusters is higher than that in the field. The radiation enhancement is consistent with a substantially higher surface brightness of the X-ray emission detected from coronae in the cluster environment. The total X-ray luminosity of a corona, however, depends on the relative importance of the surrounding thermal and ram pressures. These environment dependences should at least partly explain the large dispersion in the observed diffuse X-ray luminosities of spheroids with similar stellar properties. Furthermore, we show that an outflow powered by the distributed feedback can naturally produce a positive radial gradient in the hot gas entropy, mimicking a cooling flow.