A linear residual structure across galaxy rotation curves

Abstract

Galaxy rotation curves exhibit systematic discrepancies between the observed dynamics and the gravitational contribution expected from baryonic matter. Identifying empirical regularities in these discrepancies may provide insight into the organization of galaxy dynamics. We investigate whether the residual component of galaxy rotation curves contains a common structure across galaxies spanning a broad range of masses and morphologies. Using rotation-curve data from the SPARC and LITTLE THINGS surveys, we analyze residual velocity-squared profiles after accounting for the baryonic contribution and allowing for uncertainties in the baryonic normalization. We find that the residuals are not randomly distributed but instead follow a common linear pattern across a diverse galaxy population. Population-level analysis shows that the data preferentially select this linear residual structure over alternative radial dependences. The residual component separates into a mass-coupled contribution and a second contribution that remains nearly independent of galaxy mass. These empirical trends are observed across both spiral and dwarf galaxy samples. The existence of a common residual structure across galaxies spanning a broad range of masses and morphologies provides a new empirical constraint on theories of galaxy dynamics.