Outflows and extended [CII] halos in high redshift galaxies

Recent stacked ALMA observations have revealed that normal, star-forming galaxies at z ≈ 6 are surrounded by extended (≈10 kpc) [CII]-emitting haloes, which are not predicted by the most advanced, zoom-in simulations. We present a model in which these haloes are the result of supernova-driven cooling outflows. Our model contains two free parameters, the outflow mass loading factor, η, and the parent galaxy dark matter halo circular velocity, vc. The outflow model successfully matches the observed [CII] surface brightness profile if η = 3.20 ± 0.10 and vc = 170 ± 10 km s−1, corresponding to a dynamical mass of ≈1011 M. The predicted outflow rate and velocity range are 128 ± 5 M yr−1 and 300–500 km s−1, respectively. We conclude that (a) extended haloes can be produced by cooling outflows; (b) the large η value is marginally consistent with starburst-driven outflows, but it might indicate additional energy input from active galactic nuclei; and (c) the presence of [C II] haloes requires an ionizing photon escape fraction from galaxies fesc << 1. The model can be readily applied also to individual high-z galaxies, as those observed, e.g. by the ALMA ALPINE survey now becoming available.