Revision 1

Accepted · first revision · record

Title: What is the intrinsic scatter of the radial acceleration relation?
Plain: If the universal curve has no spread at all beyond measurement errors, that would favor modified gravity. If it has a real spread that depends on galaxy history, that would favor dark matter.
Precise: Measure the intrinsic scatter (in dex) of $\log g_{\mathrm{obs}}$ at fixed $\log g_{\mathrm{bar}}$, after marginalizing over distance, inclination and stellar mass-to-light ratio, for rotation curves and for weak lensing out to $\sim 1\ \mathrm{Mpc}$. MOND predicts zero scatter and no residual dependence on galaxy properties; LCDM predicts nonzero scatter tied to halo concentration and formation history. An answer is the scatter with uncertainty below $0.02\ \mathrm{dex}$ and the residual correlations.
Settled by: A homogeneous rotation-curve sample with independent distances plus stacked galaxy-galaxy weak lensing at low acceleration.
Kind: well-posed
Answer type: value
References: (empty)
Literature status: contested
Status note: 2024 weak-lensing analyses reported the relation and flat implied rotation curves extending to several hundred kpc (moderate confidence).
Posed since: (empty)