2017MNRAS.470.1086C

Under Newtonian gravity, total masses for dSph galaxies will scale as M_T ∝ R_eσ², with R_e the effective radius and σ their velocity dispersion. When both of the above quantities are available, the resulting masses are compared to observed stellar luminosities to derive Newtonian mass-to-light ratios (M/L), given a physically motivated proportionality constant in the above expression. For local dSphs and the growing sample of ultrafaint such systems, the above results in the largest (M/L) of any galactic systems known, with values in the hundreds and even thousands being common. The standard interpretation is for a dominant presence of an as yet undetected dark matter component. If, however, reality is closer to a MONDian theory at the extremely low accelerations relevant to such systems, σ will scale with stellar mass M_*^1/4. This yields an expression for the mass-to-light ratio that will be obtained under Newtonian assumptions of (M/L)_N = 120R_e(U_*/L)^1/2. Here, we compare (M/L)_N values from this expression to Newtonian inferences for this ratios for the actual (R_e, σ, L) observed values for a sample of recently observed ultrafaint dSphs, obtaining good agreement. Then, for systems where no σ values have been reported, we give predictions for the (M/L)_N values, which under a MONDian scheme are expected once kinematical observations become available. For the recently studied Dragonfly 44 and Crater II systems, reported (M/L)_N values are also in good agreement with MONDian expectations.