The Relation Between Stellar and Dynamical Surface Densities in the Central Regions of Disk Galaxies

ABSTRACT We use the Spitzer Photometry and Accurate Rotation Curves (SPARC) database to study the relation between the central surface density of stars Σ ⋆ ( 0 ) and dynamical mass Σ dyn ( 0 ) in 135 disk galaxies (S0 to dIrr). We find that Σ dyn ( 0 ) correlates tightly with Σ ⋆ ( 0 ) over 4 dex. This central density relation can be described by a double power law. High surface brightness galaxies are consistent with a 1:1 relation, suggesting that they are self-gravitating and baryon dominated in the inner parts. Low surface brightness (LSB) galaxies systematically deviate from the 1:1 line, indicating that the dark matter contribution progressively increases but remains tightly coupled to the stellar one. The observed scatter is small (∼0.2 dex) and largely driven by observational uncertainties. The residuals show no correlations with other galaxy properties like stellar mass, size, or gas fraction.