The Alpine-Alma [Cii] Survey: Size Of Individual Star-Forming Galaxies At Z=4-6 And Their Extended Halo Structure

Abstract We present the physical extent of [C ii ] 158 μ m line-emitting gas from 46 star-forming galaxies at z = 4–6 from the ALMA Large Program to INvestigate C ii at Early Times (ALPINE). Using exponential profile fits, we measure the effective radius of the [C ii ] line ( ) for individual galaxies and compare them with the rest-frame ultraviolet (UV) continuum ( ) from Hubble Space Telescope images. The effective radius exceeds by factors of ∼2–3, and the ratio of increases as a function of M star . We do not find strong evidence that the [C ii ] line, rest-frame UV, and far-infrared (FIR) continuum are always displaced over ≃1 kpc scale from each other. We identify 30% of isolated ALPINE sources as having an extended [C ii ] component over 10 kpc scales detected at 4.1 σ –10.9 σ beyond the size of rest-frame UV and FIR continuum. One object has tentative rotating features up to ∼10 kpc, where the 3D model fit shows the rotating [C ii ]-gas disk spread over 4 times larger than the rest-frame UV-emitting region. Galaxies with the extended [C ii ] line structure have high star formation rate, high stellar mass ( M star ), low Ly α equivalent width, and more blueshifted (redshifted) rest-frame UV metal absorption (Ly α line), as compared to galaxies without such extended [C ii ] structures. Although we cannot rule out the possibility that a selection bias toward luminous objects may be responsible for such trends, the star-formation-driven outflow also explains all these trends. Deeper observations are essential to test whether the extended [C ii ] line structures are ubiquitous to high- z star-forming galaxies.