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

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 S /L V ) based on the high-resolution neutral hydrogen (H i) observations of the SMC. We adopt both the Burkert and the Navarro-Frenk-White (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 dm ) and the mean density (ρ dm ) of the dark matter halo within the optical radius (∼3 kpc) of the SMC can be significantly low for M S /L V = 2-4 reasonable for a galaxy dominated by older stellar populations. For example, the estimated M dm and ρ dm are 7.5 x 10 7 M ⊙ and 6.7 x 10 -4 M ⊙ pc -3 , respectively, for M S /L V = 3.8. The models with lower M S /L V ( 1 kpc) (thus a low density) and a large mass (M d m > 3 x 10 9 M ⊙ ) can be better fit to the observed slowly rising rotation curve than the NFW one for a reasonable M S /L V ∼2. 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. We suggest that the dark mater halo of the SMC is likely to have the initial total mass and core radius as large as, or larger than, 6.5 x 10 9 M ⊙ and 3.2 kpc, respectively. We discuss limitations of the present model in estimating the total mass of the SMC.