JWST/MIRI unveils the stellar component of the GN20 dusty galaxy overdensity at z=4.05

Despite the importance of the dusty star-forming galaxies (DSFGs) at z>2 for understanding the galaxy evolution in the early Universe, their stellar distributions traced by the near-IR emission were spatially unresolved until the arrival of the JWST. In this work we present, for the first time, a spatially-resolved morphological analysis of the rest-frame near-IR ( 1.1-3.5μm) emission in DSFGs traced with the JWST/MIRI. In particular, we study the mature stellar component for the three DSFGs and a Lyman-break galaxy (LBG) present in an overdensity at z=4.05. Moreover, we use MIRI images along with UV to (sub)-mm ancillary photometric data to model their SEDs and extract their main physical properties. The sub-arcsec resolution MIRI images have revealed that the stellar component present a wide range of morphologies, from disc-like to compact and clump-dominated structures. These near-IR structures contrast with their UV emission, which is usually diffuse and off-centered. The SED fitting analysis shows that GN20 dominates the total SFR with a value  2500 M_⊙yr^-1 while GN20.2b has the highest stellar mass in the sample (M_* 2×10^11 M_⊙). The two DSFGs classified as LTGs (GN20 and GN20.2a) show high specific SFR (sSFR>30 Gyr^-1) placing them above the star-forming main sequence (SFMS) at z 4 by >0.5 dex while the ETG (i.e.,GN20.2b) is compatible with the high-mass end of the main sequence. When comparing with other DSFGs in overdensities at z 2-7 we observe that our objects present similar SFRs, depletion times and projected separations. Nevertheless, the effective radii computed for our DSFGs ( 3 kpc) are up to two times larger than those of isolated galaxies observed in CEERS and ALMA-HUDF at similar redshifts. We interpret this difference as an effect of rapid growth induced by the dense environment.