Exploring the Dark Matter Disc Model in Dwarf Galaxies: Insights from the LITTLE THINGS Sample

TL;DR

This study compares dark matter disc and standard halo models in dwarf galaxies, finding similar fit quality but significantly lower galaxy mass estimates in the dark matter disc model, supporting a flat-core rotation profile.

Contribution

It introduces and tests the dark matter disc model against the standard halo model using dwarf galaxy velocity data, highlighting differences in inferred galaxy masses.

Findings

Dark matter disc fits are statistically comparable to standard halo fits.

Galaxy masses inferred from the DMD model are 10-100 times smaller.

Inner rotation curves are consistent with a flat-core profile in the DMD framework.

Abstract

We conducted an analysis of the velocity field of dwarf galaxies in the LITTLE THINGS sample, focusing on deriving 2D velocity maps that encompass both the transverse and radial velocity fields. Within the range of radial distances where velocity anisotropies are sufficiently small for the disc to be considered rotationally supported, and where the warped geometry of the disc can be neglected, we reconstructed the rotation curve while taking into account the effect of the asymmetric drift. To fit the rotation curves, we employed the standard halo model and the dark matter disc (DMD) model, which assumes that dark matter is primarily confined to the galactic discs and can be traced by the distribution of \HI{}. Interestingly, our analysis revealed that the fits from the DMD model are statistically comparable to those obtained using the standard halo model, but the inferred masses of the galaxies in the DMD model are approximately 10 to 100 times smaller than the masses inferred in the standard halo model. In the DMD model, the inner slope of the rotation curve is directly related to a linear combination of the surface density profiles of the stellar and gas components, which generally exhibit a flat core. Consequently, the observation of a linear relationship between the rotation curve and the radius in the disc central regions is consistent with the framework of the DMD model.