Testing subhalo abundance matching with galaxy kinematics

ABSTRACT The rotation velocities of disc galaxies trace dark matter halo structure, providing direct constraints on the galaxy–halo connection. We construct a Bayesian forward model to connect the dark matter halo population predicted by Lambda-cold dark matter with an observed sample of disc galaxies from the Spitzer Photometry and Accurate Rotation Curves (SPARC) database through their maximum rotation velocities. Our approach combines a subhalo abundance matching scheme (accounting for assembly bias) with a parametrized halo response to galaxy formation. When assuming no correlation between selection in the SPARC survey and halo properties, reproducing the observed velocities requires strong halo expansion, low abundance matching scatter, and a halo proxy that strongly suppresses the stellar masses in satellite haloes. This is in clear tension with independent clustering constraints. Allowing for SPARC-like galaxies to preferentially populate low $V_\mathrm{max}$ haloes at fixed virial mass greatly improves the goodness of fit and resolves these tensions: the preferred halo response shifts to mild contraction, the abundance matching scatter constraint relaxes to $\sigma _\mathrm{SHAM}\lt 0.30$ dex at $1\sigma$ and the proxy becomes consistent with clustering. However, the inferred selection threshold is extreme, implying that SPARC galaxies occupy the lowest ${\sim }15$ per cent of the $V_\mathrm{max,halo}$ distribution at fixed $M_\mathrm{vir}$. Moreover, even with selection, the inferred scatter remains in statistical disagreement with the low-mass clustering constraints, which are most representative of the SPARC galaxies in our sample. Our analysis highlights the advantage of augmenting clustering-based constraints on the galaxy–halo connection with kinematics and suggests a possible tension using current data.