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Researchers analyzed rotation curves from 175 SPARC galaxies and 22 LITTLE THINGS dwarf irregular galaxies, finding that deviations from Newtonian predictions follow a systematic pattern when expressed as residuals in velocity-squared space. Massive galaxies occupy a high-intercept branch where the residual intercept scales with baryonic mass to the 0.72 power, while dwarf irregular galaxies show systematically suppressed residual intercepts, with some consistent with zero. This reveals that rotation-curve residuals are not random scatter but organize into a simple, population-dependent empirical relationship with an approximately linear form.
Why it matters
This finding suggests a fundamental yet unexplained difference in how dwarf and massive galaxies accelerate matter, which could provide new constraints for dark matter models and modified gravity theories. The systematic population-dependent pattern may help discriminate between competing explanations for galaxy rotation anomalies.
arXiv:2605.23302v2 Announce Type: replace
Abstract: Galaxy rotation curves exhibit systematic deviations from the Newtonian expectation inferred from visible matter alone. Existing phenomenological descriptions capture many aspects of these deviations, but a common residual structure across massive disks and dwarf irregular galaxies remains unclear. We investigate whether rotation-curve residuals organize into a simple empirical form across the SPARC and LITTLE THINGS samples. We analyze 175 SPARC galaxies and 22 LITTLE THINGS dwarf irregular galaxies in velocity-squared space after subtracting a leading Newtonian-like term. We fit a generalized residual family, v^2-A/r=B+Cr^{q+1}, and examine which radial scaling is selected by the data. The galaxy population systematically favors the limit (qsimeq0), corresponding to an approximately linear residual relation, (v^2-A/r=B+Cr). SPARC galaxies generally occupy a high-(B) branch, whereas LITTLE THINGS dwarf galaxies show suppressed residual intercepts, including several systems consistent with (B=0). For the SPARC sample, the high-(B) branch approximately follows (Bpropto M_{rm bar}^{0.72}). {Rotation-curve residuals are not featureless scatter beyond the leading Newtonian-like contribution, but instead show a simple population-dependent empirical organization across massive and dwarf galaxy systems.}
Source: Rotation-curve residuals reveal a suppressed acceleration branch in dwarf galaxies