Dark matter dominated dwarf disc galaxy Segue 1

TL;DR

This paper models the dwarf galaxy Segue 1 as a dark matter dominated disc galaxy, estimating its physical parameters and highlighting the necessity of a massive dark matter halo to explain its observed dynamics and stability.

Contribution

It applies the dynamic model of Xiang-Gruess, Lou & Duschl to estimate the dark matter halo mass of Segue 1, considering magnetic fields and disc rotation effects, which is a novel approach.

Findings

A massive dark matter halo is required for disc equilibrium.

Estimated dark matter mass aligns with observational inferences.

Magnetic fields significantly influence the potential ratio between dark matter and baryons.

Abstract

Several observations reveal that dwarf galaxy Segue 1 has a dark matter (DM) halo at least ~ 200 times more massive than its visible baryon mass of only ~ 103 solar masses. The baryon mass is dominated by stars with perhaps an interstellar gas mass of < 13 solar masses. Regarding Segue 1 as a dwarf disc galaxy by its morphological appearance of long stretch, we invoke the dynamic model of Xiang-Gruess, Lou & Duschl (XLD) to estimate its physical parameters for possible equilibria with and without an isopedically magnetized gas disc. We estimate the range of DM mass and compare it with available observational inferences. Due to the relatively high stellar velocity dispersion compared to the stellar surface mass density, we find that a massive DM halo would be necessary to sustain disc equilibria. The required DM halo mass agrees grossly with observational inferences so far. For an isopedic magnetic field in a gas disc, the ratio f between the DM and baryon potentials depends strongly on the magnetic field strength. Therefore, a massive DM halo is needed to counteract either the strong stellar velocity dispersion and rotation of the stellar disc or the magnetic Lorentz force in the gas disc. By the radial force balances, the DM halo mass increases for faster disc rotation.