Ionized absorbers as evidence for supernova-driven cooling of the lower galactic corona

Abstract

We show that the ultraviolet absorption features, newly discovered in Hubble Space Telescope spectra, are consistent with being formed in a layer that extends a few kpc above the disk of the Milky Way. In this interface between the disk and the Galactic corona, high-metallicity gas ejected from the disk by supernova feedback can mix efficiently with the virial-temperature coronal material. The mixing process triggers the cooling of the lower corona down to temperatures encompassing the characteristic range of the observed absorption features, producing a net supernova-driven gas accretion onto the disk at a rate of a few M ⊙ yr-1. We speculate that this mechanism explains how the hot mode of cosmological accretion feeds star formation in galactic disks. © 2013. The American Astronomical Society. All rights reserved..