Environmental Effects and Size–Mass Relations of Red Disk Galaxies at 0.1 &lt; <i>z</i> &lt; 0.5

Abstract Red disk galaxies (RDGs), as a minority population in the process of galaxy evolution, have attracted considerable attention, due to the decoupling between color and morphological evolution. From the DESI Legacy Imaging Surveys, we construct an RDG sample of 75,170 galaxies and a control sample of ∼2.6 million blue disk galaxies (BDGs) at 0.1&lt; z &lt; 0.5. The RDGs exhibit a more compact structure, with a smaller size at a fixed stellar mass, manifested in the size–mass relation as a significant difference in the intercept between BDGs and RDGs. Additionally, we obtain a BDG subsample with similar mass distribution to the RDG sample through a mass-matching algorithm, and their size–mass relations exhibit similar slopes, implying that the RDGs and BDGs may have similar mass growth histories. Our analysis of the size–mass relations in cluster and field environments at 0.1 &lt; z &lt; 0.3 reveals significant environmental differences, supporting a scenario where RDG formation is driven by environmental mechanisms like ram pressure and tidal stripping. This is consistent with the observed higher RDG abundance in clusters. Overall, our results suggest that RDGs may be descendants of massive BDGs. The evolution of BDGs into RDGs is primarily driven by the asynchrony between color transformation and morphological evolution, a process accelerated by mergers, “downsizing,” ram pressure, and tidal interactions.