On the Presence of Angular-Velocity Offsets in Disk Galaxies

TL;DR

This paper proposes that the discrepancy in galactic rotation curves can be explained by a constant angular-velocity offset, leading to a new dark-halo profile that is closely related to baryonic matter and fits observational data well.

Contribution

It introduces a novel constant angular-velocity offset model that better explains rotation curve discrepancies and derives a new dark-halo profile linked to baryonic distribution.

Findings

The angular-velocity discrepancy is approximately constant across radii.

The new model outperforms traditional dark-halo profiles in fitting rotation curves.

The derived dark-halo profile encodes baryonic distribution, indicating a close baryon-dark matter relationship.

Abstract

The well-known discrepancy in galactic rotation curves refers to the mismatch between observed rotational velocities and the velocities predicted by baryonic matter. In this study we investigate a potential pattern in the discrepancy, which may point to an underlying pattern in dark-halo distributions. By looking at rotational-velocity curves from an alternate perspective, the angular-velocity curves, it appears that the observed angular velocities and their corresponding baryonic predictions differ by a constant shift. That is, the discrepancy may be reduced to a constant angular-velocity term, independent of the radius. We test the generality of the suggested property by analysing 143 high-quality rotation curves. The property appears significant as it performs equally well (or better) than well-established dark-halo models. Compared to a Burkert profile, it is preferred in 60% of the cases, while relative to a Navarro Frenk White profile (NFW), it is superior in 73% of the cases. Next, by including the new phenomenological property within the dynamical equations, we find an explicit expression for the dark-halo profile. The new single-parameter profile is characterised by a remarkable property: it is intrinsically related to the baryonic distribution. Thus, information regarding the cuspy or cored nature of a particular dark halo, according to this profile, is encoded (and explicitly determined) by the respective baryonic behaviour.