The multiwavelength structure of post-starburst galaxies at 0.5 < z < 3 with JWST PRIMER: compact morphologies and residual disturbances

Abstract

We investigate the multiwavelength structure of recently-quenched post-starburst (PSB) galaxies at (Formula presented), using photometrically selected samples from the Ultra Deep Survey. Leveraging deep eight-band James Webb Space Telescope/NIRCam imaging from the PRIMER programme, we analyse (Formula presented) PSBs across the rest-frame optical–to–near-infrared, and compare with a reference sample of (Formula presented) passive and star-forming galaxies. Structural parameters (effective radius (Formula presented) and Sérsic index n) are derived independently in each waveband, and reveal that PSBs exhibit minimal structural variation with wavelength, indicating negligible stellar population age gradients or internal dust obscuration. We confirm that PSBs follow the established redshift–mass trends: at (Formula presented), massive PSBs ((Formula presented) ) are compact spheroids resembling massive passive galaxies, albeit significantly more compact, whereas at (Formula presented), PSBs are typically low-mass ((Formula presented) ) compact, disc-dominated systems akin to low-mass passive discs. Furthermore, for the first time, we systematically quantify disturbance indicators (residual flux fraction (Formula presented), asymmetry, residual asymmetry) across a large PSB sample. At all masses, PSBs exhibit low (Formula presented) and asymmetry values comparable to passive systems and consistent with smooth, largely undisturbed morphologies. However, at (Formula presented), massive PSBs ((Formula presented) ) show enhanced residual asymmetry relative to the passive population, indicating a previously unrecognized level of structural disturbance masked beneath a smooth stellar distribution. These results suggest that, while structural transformation is largely complete by the PSB phase, residual disturbances persist at high redshift, supporting a scenario in which rapid quenching proceeds via two distinct pathways: highly disruptive events (e.g. major mergers) at high z and high mass, and comparatively gentle processes at later times.