The ALPINE-ALMA [CII] Survey: Size of Individual Star-forming Galaxies at z=4-6 and Their Extended Halo Structure

We present the physical extent of [C II] 158 mu 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 (r(e),([C II])) for individual galaxies and compare them with the rest-frame ultraviolet (UV) continuum (re, UV) from Hubble Space Telescope images. The effective radius r(e),([C II]) exceeds r(e, UV) by factors of similar to 2-3, and the ratio of r(e),([C II])/r(e, UV) 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 similar or equal to 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 4.1s-10.9s beyond the size of rest-frame UV and FIR continuum. One object has tentative rotating features up to similar 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 alpha equivalent width, and more blueshifted (redshifted) rest-frame UV metal absorption (Ly alpha 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.