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

Year: 2022

DOI: 10.3847/1538-4357/ac7a47

We present the average [C ii] 158 μm emission line sizes of UV-bright star-forming galaxies at z ∼ 7. Our results are derived from a stacking analysis of [C ii] 158 μm 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 ∼ 7 has an effective radius rₑ of 2.2 ± 0.2 kpc. It is ≳ 2× larger than the dust continuum and the rest-frame UV emission, in agreement with recently reported measurements for z ≲ 6 galaxies. Additionally, we compared the average [C ii] size with 4 z ii] at Early times (ALPINE). By analyzing [C ii] sizes of 4 z ii] size of rₑ = 2.2 ± 0.2 kpc and rₑ = 2.5 ± 0.2 kpc for z ∼ 5.5 and z ∼ 4.5 galaxies, respectively. These measurements show that star-forming galaxies, on average, show no evolution in the size of the [C ii] 158 μm emitting regions at redshift between z ∼ 7 and z ∼ 4. This finding suggests that the star-forming galaxies could be morphologically dominated by gas over a wide redshift range.