The Universal Rotation Curve of Spiral Galaxies: I. the Dark Matter Connection

TL;DR

This study analyzes a large sample of spiral galaxy rotation curves to reveal a universal pattern governed by luminosity, highlighting the role of dark matter in shaping galaxy mass profiles and their scaling relations.

Contribution

It demonstrates the existence of a universal rotation curve for spirals and details the scaling relations between dark matter and luminous matter properties, emphasizing dark matter's dominance in low-luminosity galaxies.

Findings

Rotation curves depend strongly on luminosity.

Dark matter dominates in low-luminosity galaxies.

Scaling relations link dark matter properties with galaxy luminosity.

Abstract

We use a homogeneous sample of about 1100 rotation curves (RCs) and relative surface photometry to investigate (out to 2 optical radii and over 6 mag) the main mass structure properties of spirals. We confirm the strong dependence on luminosity for both the profile and the amplitude of RCs. Spiral RCs show the striking feature that a single parameter, the luminosity, dictates the rotation velocity at any radius for all objects, so revealing the existence of a universal RC. At high luminosity, there is a slight discrepancy between the profiles of RCs and those predicted from the luminous matter (LM) distributions: this implies a small, yet detectable, amount of dark matter (DM). At low luminosities the failure of the LM prediction is most severe, and DM is the only relevant mass component. Some of the derived scaling properties between dark and luminous galactic structure parameters are: (a) the DM/LM mass ratio at the optical radius scales inversely with luminosity; (b) the halo core radius is comparable to the optical radius, but shrinks for lower luminosities; (c) the central halo density scales as L^{-0.7}; (d) the halo virial mass scales as L^{0.5}. Such scaling properties can be represented as a curve in the luminosity-(DM/LM ratio)-(DM core radius)-(central DM density) space, which acts as the spirals' counterpart to the FP of ellipticals.