A dynamical–photometric phase space for spiral galaxies: probing the local coupling between light and gravity

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ID: 321898
2026
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Abstract
ABSTRACT The interplay between luminous matter distribution and the local gravitational field within disc galaxies encodes physical information beyond that captured by global scaling relations. We introduce a dynamical–photometric phase space defined by the kinematic variable $X(R)=V(R)/R$ and the photometric variable $Y(R)=\mathrm{d}\ln I/\mathrm{d}\ln R$, placing the local gravitational scale and the logarithmic surface brightness gradient into direct pointwise correspondence at each galactocentric radius R. The quantity $X=V/R=\omega$ represents the angular frequency of circular motion and acts as a probe of the local mean mass density, while Y measures the radial steepness of the stellar light distribution. The baryon-dominated inner disc is characterized by large negative Y, whereas the dark-matter-dominated outer region approaches $Y\rightarrow 0$. This two-regime behaviour is described by the smooth sigmoid relation $Y=[a\ln X+b]/(1+\exp [k(X-X_{\rm trans})])$, which reduces to the logarithmic coupling $Y=a\ln X+b$ in the baryonic zone. We apply this framework to 136 late-type galaxies from the Spitzer Photometry and Accurate Rotation Curves data base, spanning inclinations $20^{\circ }$–$89^{\circ }$, distances 1–130 Mpc, and five decades in stellar mass. The median coefficient of determination is $R^{2}=0.930$. Statistical validation includes eight independent tests together with five-fold cross-validation. The transition parameter $X_{\rm trans}$ identifies the onset of dark-matter dominance, corresponding to a median transition radius $R_{\rm trans}=5.40$ kpc across the sample.
Reference Key
openalex_W7170049210 Use this key to autocite in the manuscript while using SciMatic Manuscript Manager or Thesis Manager
Authors Aritra Sanyal, Farook Rahaman
Journal monthly notices of the royal astronomical society
Year 2026
DOI
10.1093/mnras/stag1270
URL
https://doi.org/10.1093/mnras/stag1270
Keywords Keywords not found

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