Dark Halos Predicted from the Baryonic Radial Transitions in Galaxies

Abstract

Galaxy rotation curves show a systematic mismatch between the observed circular field and the field predicted from baryons alone. Standard models close this mismatch by fitting a dark halo. This paper tests a different possibility: that the residual field is not an arbitrary halo profile, but a baryonically ordered geometry. We define the residual field from SPARC rotation curves and locate the first upward transition where the residual becomes comparable to the baryonic field. From that transition point, the outer residual profile is described by a power-law slope gamma. In SPARC, 124 of 175 galaxies show this transition. The outer residual slope is strongly correlated with the baryonic velocity at the transition: Spearman rho = 0.725 in the quality sample and rho = 0.801 for Q=1 galaxies. A synthetic independent-halo null, processed through the same transition pipeline, does not recover the observed correlation. The key predictive test is leave-one-galaxy-out reconstruction. Using the baryonic transition relation learned from the other galaxies, the method reconstructs 1096 held-out outer velocity points with a mean absolute error of 7.71 km/s, outperforming RAR and NFW baselines on the same exterior domain. The result suggests that the outer structure usually assigned to a dark halo is not a free shape independent of baryons. Its radial width is encoded in the baryonic transition and central depth: compact or deep baryonic structures yield steeper residual profiles, while diffuse structures yield broader ones. A full reproducibility package is included.