The Effect of Adiabatic Compression on Dark Matter Halos and the Radial Acceleration Relation

Abstract

We use a semi-empirical model to investigate the radial acceleration relation (RAR) in a cold dark matter (CDM) framework. Specifically, we build 80 model galaxies covering the same parameter space as the observed galaxies in the SPARC database, assigning them to dark matter halos using abundance matching and halo mass-concentration relations. We consider several abundance matching relations, finding some to be a better match to the kinematic data than others. We compute the unavoidable gravitational interactions between baryons and their dark matter halos, leading to an overall compression of the original NFW halos. Before halo compression, high-mass galaxies approximately lie on the observed RAR whereas low-mass galaxies display up-bending "hooks" at small radii due to DM cusps, making them deviate systematically from the observed relation. After halo compression, the initial NFW halos become more concentrated at small radii, making larger contributions to rotation curves. This increases the total accelerations, moving all model galaxies away from the observed relation. These systematic deviations suggest that the CDM model with abundance matching alone cannot explain the observed RAR. Further effects (e.g., feedback) would need to counteract the compression with precisely the right amount of halo expansion, even in high mass galaxies with deep potential wells where such effects are generally predicted to be negligible.

The scatter in the galaxy-halo connection: a machine learning analysis

“…While the earliest models used present-day virial mass as the proxy (Conroy et al 2006;Moster et al 2010;Behroozi et al 2010), more recent work has shown that fits to galaxy clustering are improved by instead using a quantity that scales with haloes' concentration (Reddick et al 2013;Lehmann et al 2017); this reflects, through the correlation of concentration and halo formation time, the fact that galaxies formed in haloes at 𝑧 > 0. SHAM also provides reasonable fits to galaxies' dynamical scaling relations, although there are indications that the galaxy mass-halo mass relation it implies is too curved and that the neglect of additional correlations in the galaxy-halo connection generates excess scatter in circular velocity at fixed mass (Trujillo-Gomez et al 2011;Desmond & Wechsler 2015Desmond 2017a,b;Li et al 2022).…”