The Intrinsic Scatter of the Radial Acceleration Relation
  We present a detailed Monte Carlo model of observational errors in observed
galaxy scaling relations to recover the intrinsic (cosmic) scatter driven by
galaxy formation and evolution processes. We apply our method to the stellar
radial acceleration relation (RAR) which compares the local observed radial
acceleration to the local Newtonian radial acceleration computed from the
stellar mass distribution. The stellar and baryonic RAR are known to exhibit
similar scatter. Lelli+2017 (L17) studied the baryonic RAR using a sample of
153 spiral galaxies and inferred a negligible intrinsic scatter. If true, a
small scatter might challenge the LCDM galaxy formation paradigm, possibly
favoring a modified Newtonian dynamics interpretation. The intrinsic scatter of
the baryonic RAR is predicted by modern LCDM simulations to be ~0.06-0.08 dex,
contrasting with the null value reported by L17. We have assembled a catalog of
structural properties with over 2500 spiral galaxies from six deep imaging and
spectroscopic surveys (called PROBES for the "Photometry and Rotation curve
OBservations from Extragalactic Surveys") to quantify the intrinsic scatter of
the stellar RAR and other scaling relations. The stellar RAR for our full
sample has a median observed scatter of 0.17 dex. We use our Monte Carlo
method, which accounts for all major sources of measurement uncertainty, to
infer a contribution of 0.12 dex from the observational errors. The intrinsic
scatter of the stellar RAR is thus estimated to be 0.11$\pm$0.02 dex, in
agreement with, though slightly greater than, current LCDM predictions.
