• galaxies: evolution
• galaxies: formation
• galaxies: high-redshift
• galaxies: ISM

Recent ALMA observations have revealed that normal, star-forming galaxies at z = 4-6 are surrounded by extended (10-15 kpc) [CII]-emitting halos; the most advanced cosmological simulations fail to reproduce the observed [CII] surface brightness, thus this discovery raises a number of thorny theoretical questions involving the formation and survival of such halo.

In this work, we explore the possibility that these halos are the result of supernovae-driven cooling outflows, by developing models that consider as main parameters the outflow mass loading factor, the galaxy star formation rate, and the dark matter halo mass. We carefully compare the predictions of our model with the results from the ALMA ALPINE sample, running an MCMC to study the posterior distribution of our parameters. The results of this comparison suggest that mass loading factors for high-z, normal star-forming galaxies lie in the range 3−10, with higher values for lower-mass and lower-SFR systems.

Our main conclusions are that (a) extended halos can indeed be produced by outflows that undergo catastrophic radiative cooling within the central kpc; (b) the large mass loading factor values are marginally consistent with starburst-driven outflows, allowing for the possibility that additional energy input from active galactic nuclei; (c) the presence of [C II] haloes requires an ionizing photon escape fraction from galaxies much lower than unity.