MIDIS. Near-infrared rest-frame morphology of massive galaxies at \(3<z<5.5\) in the Hubble eXtreme Deep Field

Thanks to decades of observations using HST, the structure of galaxies at redshift \(z>2\) has been widely studied in the rest-frame ultraviolet regime, which traces recent star formation from young stellar populations. But, we still have little information about the spatial distribution of the older, more evolved, stellar populations, constrained by the rest-frame infrared portion of galaxies' spectral energy distribution. We present the morphological characterization of a sample of 21 massive galaxies (\(\log(M_{\star}/M_{\odot})>9.5\)) at redshift \(34\) later-type morphologies compared to \(z\sim3\) galaxies. These findings suggest a transition phase in galaxy assembly and central mass build up already taking place at \(z\sim3-4\). MIRI provides unique information about the structure of the mature stellar population of high-redshift galaxies, unveiling that massive galaxies beyond cosmic noon are prevalently compact disk galaxies with smooth mass distribution.