The Variation of Rotation Curve Shapes as a Signature of the Effects of Baryons on Dark Matter Density Profiles

TL;DR

This study investigates how baryonic effects influence dark matter density profiles by analyzing galaxy rotation curves, showing that models incorporating baryonic processes better match observed variations than universal NFW profiles.

Contribution

The paper demonstrates that baryonic processes significantly affect dark matter density profiles, explaining the observed scatter in galaxy rotation curve shapes better than universal profiles.

Findings

Models with baryonic effects match observed rotation curve scatter.

Universal NFW profiles cannot reproduce the lowest Vrot(1kpc)/Vmax values.

Mass-dependent profiles influenced by baryons explain the data well.

Abstract

Rotation curves of galaxies show a wide range of shapes, which can be paramaterized as scatter in Vrot(1kpc)/Vmax i.e.the ratio of the rotation velocity measured at 1kpc and the maximum measured rotation velocity. We examine whether the observed scatter can be accounted for by combining scatters in disc scale-lengths, the concentration-halo mass relation, and the M*-Mhalo relation. We use these scatters to create model galaxy populations; when housed within dark matter halos that have universal, NFW density profiles, the model does not match the lowest observed values of Vrot(1kpc)/Vmax and has too little scatter in Vrot(1kpc)/Vmax compared to observations. By contrast, a model using a mass dependent dark matter profile, where the inner slope is determined by the ratio of M*/Mhalo, produces galaxies with low values of Vrot(1kpc)/Vmax and a much larger scatter, both in agreement with observation. We conclude that the large observed scatter in Vrot(1kpc)/Vmax favours density profiles that are significantly affected by baryonic processes. Alternative dark matter core formation models such as SIDM may also account for the observed variation in rotation curve shapes, but these observations may provide important constraints in terms of core sizes, and whether they vary with halo mass and/or merger history.