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 [CII] 158um line-emitting gas from 46
star-forming galaxies at z=4-6 from the ALMA Large Program to INvestigate CII
at Early Times (ALPINE). Using exponential profile fits, we measure the
effective radius of the [CII] line (r_e,[CII]) for individual galaxies and
compare them with the rest-frame ultra-violet (UV) continuum (r_e,UV) from
Hubble Space Telescope images. The effective radius r_e,[CII] exceeds r_e,UV by
factors of ~2-3 and the ratio of r_e,[CII]/r_e,UV increases as a function of
M_star. We do not find strong evidence that [CII] line, the rest-frame UV, and
FIR continuum are always displaced over ~ 1-kpc scale from each other. We
identify 30% of isolated ALPINE sources as having an extended [CII] component
over 10-kpc scales detected at 4.1$\sigma$-10.9$\sigma$ beyond the size of
rest-frame UV and far-infrared (FIR) continuum. One object has tentative
rotating features up to ~10-kpc, where the 3D model fit shows the rotating
[CII]-gas disk spread over 4 times larger than the rest-frame UV-emitting
region. Galaxies with the extended [CII] line structure have high
star-formation rate (SFR), stellar mass (M_star), low Lya equivalent-width, and
more blue-shifted (red-shifted) rest-frame UV metal absorption (Lya line), as
compared to galaxies without such extended [CII] structures. Although we cannot
rule out the possibility that a selection bias towards 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 [CII] line structures are ubiquitous to high-z star-forming galaxies.
