First Identification of 10-kpc Scale [CII] 158um Halos around Star-Forming Galaxies at z=5-7

Understand

We report the discovery of 10-kpc scale [CII] 158um halos surrounding star-forming galaxies in the early Universe.

• We choose deep ALMA data of 18 galaxies each with a star-formation rate of ~ 10-70 Msun with no signature of AGN whose [CII] lines are individually detected at z=5.153-7.142, and conduct stacking of the [CII] lines and dust-continuum in the uv-visibility plane.
• The radial profiles of the surface brightnesses show a 10-kpc scale [CII] halo at the 9.2sigma level significantly extended more than the HST stellar continuum data by a factor of ~5 on the exponential-profile basis, as well as the dust continuum.
• We also compare the radial profiles of [CII] and Lya halos universally found in star-forming galaxies at this epoch, and find that the scale lengths agree within the 1sigma level.