The ALMA REBELS Survey: Average [C ii] 158 μm Sizes of Star-forming Galaxies from z ∼ 7 to z ∼ 4
Yoshinobu Fudamoto, Renske Smit, R. A. A. Bowler, Pascal A. Oesch, R. J. Bouwens, Mauro Stefanon, Hanae Inami, Ryan Endsley, Valentino González, Sander Schouws, Daniel P. Stark, Hiddo Algera, Manuel Aravena, Laia Barrufet, Elisabete da Cunha, Pratika Dayal, Andrea Ferrara, Luca Graziani, Jacqueline Hodge, A. P. S. Hygate, Akio Inoue, Themiya Nanayakkara, A. Pallottini, Elia Pizzati, Raffaella Schneider, Laura Sommovigo, Yuma Sugahara, Michael W. Topping, P. van der Werf, M. Béthermin, P. Cassata, M. Dessauges‐Zavadsky, E. Ibar, Andreas L. Faisst, Seiji Fujimoto, M. Ginolfi, Nimish P. Hathi, Gareth C. Jones, F. Pozzi, D. Schaerer
Abstract
Abstract We present the average [C ii ] 158 μ m emission line sizes of UV-bright star-forming galaxies at z ∼ 7. Our results are derived from a stacking analysis of [C ii ] 158 μ 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 ∼ 7 has an effective radius r e 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 < 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 ∼ 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 μ m 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.