Early-type Galaxies on the Star Formation Main Sequence: Internal Star Formation Geometries Revealed with MaNGA and Their Environmental Origin

Abstract Star-forming galaxies on the main sequence (MS) are often regarded as a uniform population characterized by similar global star formation properties. However, there exists a diversity in galaxy morphologies at a fixed stellar mass and star formation rate. In this study, using spatially resolved properties from the MaNGA final data release, we classify MS galaxies into late type (MS-late) and early type (MS-early). In addition, we further divide the MS-early galaxies into two distinct subgroups based on their internal star formation and stellar mass distributions within the galaxies. The first group—“MS-early_SF”—shows centrally concentrated star formation without prominent stellar bulges and resides preferentially in dense environments, suggesting environmentally driven evolution. The second group—“MS-early_stellar”—exhibits significant stellar bulges with suppressed central star formation, maintains disk-like star formation patterns, and inhabits environments similar to those of late-type galaxies, indicating evolution through internal secular processes. Our findings demonstrate that spatially resolved observations play critical roles in revealing the diverse evolutionary pathways hidden within galaxies that share similar global properties.