Abstract
Galactic rotation curves exhibit diverse behavior in the inner regions, while obeying an organizing principle, i.e., they can be approximately described by a radial acceleration relation or the Modified Newtonian Dynamics phenomenology. We analyze the rotation curve data from the SPARC sample, and explicitly demonstrate that both the diversity and uniformity are naturally reproduced in a hierarchical structure formation model with the addition of dark matter self-interactions. The required concentrations of the dark matter halos are fully consistent with the concentration-mass relation predicted by the Planck cosmological model. The inferred stellar mass-to-light ($3.6 \mu m$) ratios scatter around $0.5 M_\odot/L_\odot$, as expected from population synthesis models, leading to a tight radial acceleration relation and baryonic Tully-Fisher relation. The inferred stellar-halo mass relation is consistent with the expectations from abundance matching. These results indicate that the inner dark matter halos of galaxies are thermalized due to the self-interactions of dark matter particles.
Highlights
Galactic rotation curves of spiral galaxies show a variety of behaviors in the inner parts, even across systems with similar halo and stellar masses, which lacks a self-consistent explanation in the standard cold dark matter (CDM)
In the Supplemental Material [32], we present self-interacting dark matter (SIDM) and modified Newtonian dynamics (MOND) fits to 135 individual galaxies from the SpitzerPhotometry and Accurate Rotation Curves (SPARC) sample and additional results that support the main text, including model fits to simulated halos
We have demonstrated that SIDM explains both the diversity and the tight radial acceleration relation (RAR) exhibited in the rotation curves, as dark matter self-interactions thermalize the inner halo in the presence of the baryonic potential
Summary
Galactic rotation curves of spiral galaxies show a variety of behaviors in the inner parts, even across systems with similar halo and stellar masses, which lacks a self-consistent explanation in the standard cold dark matter (CDM). Recent hydrodynamical simulations of galaxy formation with CDM have clearly shown that a RAR emerges [22,23,24] These simulated galaxies do not represent the full range of diversity in the SPARC data set, and they cannot yet explain the rotation curves of low- and high-surface-brightness galaxies simultaneously. We show that self-interacting dark matter (SIDM) provides a unified way to understand the diverse rotation curves of spiral galaxies while reproducing the RAR with a small scatter. (iii) For the same σ=m that addresses the diversity problem, the baryon content of the galaxies and the mass model of their host halos lead to the RAR with a scatter as small as the one in Ref. In the Supplemental Material [32], we present SIDM and MOND fits to 135 individual galaxies from the SPARC sample and additional results that support the main text, including model fits to simulated halos
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