Chemically Primitive Dwarf Accretion Reignites the Inner Disk Assembly of Malin 1

Abstract We present a detailed kinematic and stellar population analysis of the inner disk of Malin 1, a giant low surface brightness galaxy with a prominent SB 0-type central morphology. AstroSat far-ultraviolet (FUV) imaging reveals clumpy emission features indicating recent star formation. Using MUSE integral field spectroscopy, we identify four star-forming complexes (SFCs) within the inner 10 kpc, each associated with localized ionized gas emission in distinct H α velocity channels. Two of the SFCs, including a FUV clump, appear on the blueshifted side ( V H α = −230 km s −1 ), while the other two are redshifted. The FUV clump shows a strong velocity offset (∼150 km s −1 ) and high gas dispersion (∼250 km s −1 ), indicating that it is kinematically decoupled from the rotating disk. The spatial and velocity isolation of these features in the channel map confirms they do not follow regular disk rotation. The FUV clump hosts young (250–500 Myr), extremely metal-poor ([M/H] ≃ −1.69) and α -enriched ([ α /Fe] ∼ 0.5) stellar populations, sharply contrasting with the surrounding supersolar gas-phase metallicity. The young stellar populations in each SFC are chemically distinct (similar to the FUV clump) from the enriched central interstellar medium (ISM), indicating rapid, local star formation from primitive gas before efficient mixing with the enriched ISM. Their spatial and velocity segregation, age synchronicity, and chemical homogeneity suggest an origin of gas delivered by a disrupted, gas-rich dwarf on a high-inclination (off-plane) orbit. These results suggest that the central HSB within ∼9″ (14 kpc) radius component of Malin 1 has grown through discrete, externally driven accretion, contributing to its complex, hybrid disk morphology.