2025/12/24 by Nalin Dhiman, Dhiman, Nalin
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics of Galaxies (astro-ph.GA) #Computational Physics (physics.comp-ph) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies
paper · doi:10.48550/arxiv.2512.21376
openalex publication_date 2025/12/24 · openalex created_date 2025/12/30 · openalex updated_date 2026/07/28
Observed rotation curves of disk galaxies remain a sharp empirical probe of the relationship between baryons and dynamics. We study a minimal, explicitly phenomenological alternative to standard halo parameterizations: an additional inward radial acceleration proportional to the local tangential speed, a\vca(r)=γ(r) v(r), with a saturating coupling γ(r)=\vinf/(r+\rzero). Combining this ansatz with the circular-motion condition yields a quadratic equation for v(r) with a closed-form physical branch.We fit this ``velocity-coupled acceleration'' (\vca) model to Ngal=171 rotation curves from the SPARC sample using the published baryonic decompositions (gas, disk, bulge), and we compare to two commonly used two-parameter halo models (NFW and Burkert) using an identical optimization pipeline and error model.For a fiducial systematic error floor σ0=5~\mathrmkm s-1, the \vca model is typically competitive with an NFW halo and performs comparably (though not uniformly better) than a Burkert halo in information-criterion comparisons.We further perform MCMC inference for \vca parameters, quantify posterior predictive coverage, and show that parameter posteriors exhibit a strong \vinf--\rzero degeneracy for many galaxies; only 47/171 galaxies yield well-identified posteriors under simple width-based criteria. We also perform a simple radial holdout cross-validation (outer 30% of radii) and find predictive RMSE comparable to NFW and Burkert under this protocol.Finally..