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

<jats:title>Abstract</jats:title>
<jats:p>We present the physical extent of [C <jats:sc>ii</jats:sc>] 158 <jats:italic>μ</jats:italic>m line-emitting gas from 46 star-forming galaxies at <jats:italic>z</jats:italic> = 4–6 from the ALMA Large Program to INvestigate C <jats:sc>ii</jats:sc> at Early Times (ALPINE). Using exponential profile fits, we measure the effective radius of the [C <jats:sc>ii</jats:sc>] line (<jats:inline-formula>
<jats:tex-math>

</jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab94b3ieqn1.gif" xlink:type="simple"/>
</jats:inline-formula>) for individual galaxies and compare them with the rest-frame ultraviolet (UV) continuum (<jats:inline-formula>
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</jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab94b3ieqn2.gif" xlink:type="simple"/>
</jats:inline-formula>) from Hubble Space Telescope images. The effective radius <jats:inline-formula>
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<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab94b3ieqn3.gif" xlink:type="simple"/>
</jats:inline-formula> exceeds <jats:inline-formula>
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<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab94b3ieqn4.gif" xlink:type="simple"/>
</jats:inline-formula> by factors of ∼2–3, and the ratio of <jats:inline-formula>
<jats:tex-math>

</jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab94b3ieqn5.gif" xlink:type="simple"/>
</jats:inline-formula> increases as a function of <jats:italic>M</jats:italic>
<jats:sub>star</jats:sub>. We do not find strong evidence that the [C <jats:sc>ii</jats:sc>] 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 <jats:sc>ii</jats:sc>] component over 10 kpc scales detected at 4.1<jats:italic>σ</jats:italic>–10.9<jats:italic>σ</jats:italic> 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 <jats:sc>ii</jats:sc>]-gas disk spread over 4 times larger than the rest-frame UV-emitting region. Galaxies with the extended [C <jats:sc>ii</jats:sc>] line structure have high star formation rate, high stellar mass (<jats:italic>M</jats:italic>
<jats:sub>star</jats:sub>), low Ly<jats:italic>α</jats:italic> equivalent width, and more blueshifted (redshifted) rest-frame UV metal absorption (Ly<jats:italic>α</jats:italic> line), as compared to galaxies without such extended [C <jats:sc>ii</jats:sc>] 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 <jats:sc>ii</jats:sc>] line structures are ubiquitous to high-<jats:italic>z</jats:italic> star-forming galaxies.</jats:p>