Radial Profiles of Σ_*, Σ_SFR, Gas Metallicity, and Their Correlations across the Galactic Mass–Size Plane

Abstract We analyzed the global and resolved properties of approximately 1240 nearby star-forming galaxies from the MaNGA survey, comparing compact and extended galaxies—those with smaller and larger radii ( R e ), respectively—at a fixed stellar mass ( M * ). Compact galaxies typically exhibit lower H i gas fractions, higher dust extinction, higher metallicity, greater mass concentration, and lower angular momentum on a global scale. Radial profiles of stellar mass surface density (Σ * ) and star formation rate surface density (Σ SFR ) as functions of the effective radius ( R / R e ) reveal that compact galaxies display steeper gradients and higher values, resulting in elevated specific star formation rates (sSFRs) in their inner regions compared to their outskirts. At a given Σ * , compact galaxies have higher sSFRs than extended galaxies, particularly in low-mass galaxies (log( M * / M ⊙ ) ≤ 10 10 ). Additionally, their metallicity profiles differ significantly: extended galaxies have steeper metallicity gradients, while compact galaxies exhibit flatter slopes and higher metallicity at a given R / R e . After accounting for the dependence of metallicity on M * and Σ * , no further correlation with SFR is observed. The combination of higher sSFR and potentially higher star formation efficiency in compact galaxies suggests that their central gas is being rapidly consumed, leading to older stellar populations, as indicated by D n (4000) and EW(H δ A ), and resulting in faster central growth. Our results reveal that radial SFR profiles cannot be fully determined by M * and Σ * alone; other factors, such as galaxy size or angular momentum, must be considered to fully understand the observed trends.