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This study analyzed rotation curves from 175 SPARC galaxies and 22 LITTLE THINGS dwarf galaxies to identify systematic patterns in how observed rotational velocities deviate from predictions based on visible matter alone. The researchers found that when subtracting Newtonian contributions, the residuals follow a simple linear relationship (v²-A/r=B+Cr) across the galaxy population, with massive galaxies occupying a high-B branch while dwarf galaxies show suppressed residual intercepts, some consistent with B=0. This reveals that rotation-curve deviations are not random scatter but follow organized, population-dependent empirical patterns that differ systematically between massive disk galaxies and dwarf irregular systems.
Why it matters
This finding provides a new empirical framework for understanding dark matter distribution or modified gravity effects across different galaxy types. The systematic suppression of the residual intercept in dwarf galaxies compared to massive galaxies could help discriminate between competing theories and inform models of galaxy formation and evolution.
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