The ALMA REBELS Survey: Average [C ii] 158 ??m Sizes of Star-forming Galaxies from z ??? 7 to z ??? 4

We present the average [C ii] 158 mu m emission line sizes of UV-bright star-forming galaxies at z similar to 7. Our results are derived from a stacking analysis of [C ii] 158 mu m emission lines and dust continua observed by the Atacama Large Millimeter/submillimeter Array (ALMA), taking advantage of the large program Reionization Era Bright Emission Line Survey. We find that the average [C ii] emission at z similar to 7 has an effective radius r ( e ) of 2.2 +/- 0.2 kpc. It is greater than or similar to 2x larger than the dust continuum and the rest-frame UV emission, in agreement with recently reported measurements for z less than or similar to 6 galaxies. Additionally, we compared the average [C ii] size with 4 < z < 6 galaxies observed by the ALMA Large Program to INvestigate [C ii] at Early times (ALPINE). By analyzing [C ii] sizes of 4 < z < 6 galaxies in two redshift bins, we find an average [C ii] size of r (e) = 2.2 +/- 0.2 kpc and r (e) = 2.5 +/- 0.2 kpc for z similar to 5.5 and z similar to 4.5 galaxies, respectively. These measurements show that star-forming galaxies, on average, show no evolution in the size of the [C ii] 158 mu m emitting regions at redshift between z similar to 7 and z similar to 4. This finding suggests that the star-forming galaxies could be morphologically dominated by gas over a wide redshift range.