The ALMA-CRISTAL survey: Widespread dust-obscured star formation in typical star-forming galaxies at z = 4–6

We present the morphological parameters and global properties of dust-obscured star formation in typical star-forming galaxies at z = 4–6. Among 26 galaxies composed of 20 galaxies observed by the Cycle-8 ALMA Large Program, CRISTAL, and 6 galaxies from archival data, we individually detect rest-frame 158 μm dust continuum emission from 19 galaxies, 9 of which are reported for the first time. The derived far-infrared luminosities are in the range log₁₀L_IR [L_⊙] = 10.9 ‑ 12.4, an order of magnitude lower than previously detected massive dusty star-forming galaxies (DSFGs). We find the average relationship between the fraction of dust-obscured star formation (f_obs) and the stellar mass to be consistent with previous results at z = 4–6 in a mass range of log₁₀M_* [M_⊙]∼9.5 ‑ 11.0 and to show potential evolution from z = 6 ‑ 9. The individual f_obs exhibits significant diversity, and we find a potential correlation with the spatial offset between the dust and UV continuum, suggesting that inhomogeneous dust reddening may cause the source-to-source scatter in f_obs. The effective radii of the dust emission are on average ∼1.5 kpc and are about two times more extended than those seen in rest-frame UV. The infrared surface densities of these galaxies (Σ_IR ∼ 2.0 × 10¹⁰ L_⊙ kpc^‑2) are one order of magnitude lower than those of DSFGs that host compact central starbursts. On the basis of the comparable contribution of dust-obscured and dust-unobscured star formation along with their similar spatial extent, we suggest that typical star-forming galaxies at z = 4 ‑ 6 form stars throughout the entirety of their disks.