The total mass and dark halo properties of the Small Magellanic Cloud

TL;DR

This study models the dark matter halo of the Small Magellanic Cloud using HI observations and compares Burkert and NFW profiles, revealing low dark matter mass within the optical radius and implications of tidal interactions.

Contribution

It provides the first detailed modeling of the SMC's dark halo properties using high-resolution HI data and compares different dark matter profiles.

Findings

Dark matter mass within 3 kpc is low for typical stellar-to-mass-to-light ratios.

Burkert profile with a large core better fits the observed rotation curve.

Most dark halo mass may have been stripped due to tidal interactions.

Abstract

We discuss the total mass and dark halo properties of the Small Magellanic Cloud (SMC) for reasonable $V$-band stellar-to-mass-to-light ratios ($M_{\rm s}/L_{\rm V}$) based on the high-resolution neutral hydrogen (HI) observations of the SMC. We adopt both the Burkert and the NFW profiles for the dark matter halo of the SMC in order to model the radial profile of the observed rotation curve. We show that the mass ($M_{\rm dm}$) and the mean density (${\rho}_{\rm dm}$) of the dark matter halo within the optical radius ($\sim 3$ kpc) of the SMC can be significantly low for $M_{\rm s}/L_{\rm V}=2-4$ reasonable for a galaxy dominated by older stellar populations. For example, the estimated $M_{\rm dm}$ and ${\rho}_{\rm dm}$ are $7.5 \times 10^7 {\rm M}_{\odot}$ and $6.7 \times 10^{-4} {\rm M}_{\odot}$ pc$^{-3}$, respectively, for $M_{\rm s}/L_{\rm V} = 3.8$. The models with lower $M_{\rm s}/L_{\rm V}$ ($<1.0$) can show higher $M_{\rm dm}$ and ${\rho}_{\rm dm}$ yet have difficulties in reproducing the inner rotation curve profile both for the Burkert and the NFW profiles. The Burkert profile with a larger core radius ($>1$ kpc) (thus a low density) and a large mass (${\rm M}_{\rm dm} > 3 \times 10^9 {\rm M}_{\odot}$) can be better fit to the observed slowly rising rotation curve than the NFW one for a reasonable $M_{\rm s}/L_{\rm V} \sim2$. This means that most of the dark halo mass can be initially located outside the optical radius in the SMC and thus that the dark halo would have already lost a significant fraction of its original mass due to the strong tidal interactions with the Galaxy and possibly with the Large Magellanic Cloud (LMC).