2018MNRAS.480.4369P

Assuming a hydrostatic equilibrium in an H I cloud, the joint Poisson equation is set up and numerically solved to calculate the expected H I distribution. Unlike previous studies, the cloud is considered to be non-isothermal, and an iterative method is employed to estimate the intrinsic velocity dispersion profile using the observed second moment of the H I data. We apply our iterative method to a recently discovered dwarf galaxy Leo T and find that its observed H I distribution does not comply with the expected one if one assumes no dark matter in it. To model the mass distribution in Leo T, we solve the Poisson equation using a large number of trial dark matter haloes and compare the model H I surface density (Σ_ H I_) profiles to the observed one to identify the best dark matter halo parameters. For Leo T, we find a pseudo-isothermal halo with core density ρ₀ ∼ 0.67 M_☉ pc^–3 and core radius r_s ∼ 37 parsec explains the observation best. The resulting dark matter halo mass within the central 300 pc, M₃₀₀, is found to be ∼2.7 x 10⁶ M_☉. We also find that a set of dark matter haloes with similar M₃₀₀ ∼ 3.7 x 10⁶ M_☉ but very different ρ₀ and r_s values can produce an equally good Σ_ H I_ profile within the observational uncertainties. This, in turn, indicates a strong degeneracy between the halo parameters, and the best-fitting values are not unique. Interestingly, it also implies that the mass of a dark matter halo, rather than its structure, primarily directs the expected H I distribution under hydrostatic equilibrium.