Dark matter in early-type spiral galaxies: the case of NGC 2179 and of NGC 2775

TL;DR

This study analyzes the mass distribution in two early-type spiral galaxies, NGC 2179 and NGC 2775, showing that luminous matter dominates within one disk scale, with dark matter becoming significant only beyond twice that radius.

Contribution

It provides detailed kinematic modeling of two luminous spiral galaxies, challenging the idea that high-luminosity spirals are dark matter dominated at all radii.

Findings

Luminous matter accounts for all gravitating mass inside R_D.

Dark matter halo becomes significant only beyond 2 R_D.

Results oppose recent claims of universal dark matter dominance in high-luminosity spirals.

Abstract

We present stellar and ionized-gas velocity curves and velocity dispersion profiles for the Sa galaxies NGC 2179 and NGC 2775. Using their luminosity profiles and modeling both their stellar and gaseous kinematics, we have derived the mass distribution of the dark and the luminous matter. This unambiguously shows that, inside one disk length-scale R_D, the stellar bulge and disk account for the whole gravitating mass. The dark matter halo, likely present also at inner radii, becomes an important mass component only for R > 2 R_D. Giving the quantity and quality of the data, our results on these two luminous galaxies serve as strong counter-example to the recent claim according to which also high-luminosity spirals are dark matter dominated at essentially all radii.