2017MNRAS.470.1086C -
Mon. Not. R. Astron. Soc., 470, 1086-1090 (2017/September-1)
MONDian predictions for Newtonian mass-to-light ratios for ultrafaint dSphs.
CORTES R.A.M. and HERNANDEZ X.
Abstract (from CDS):
Under Newtonian gravity, total masses for dSph galaxies will scale as MT ∝ Reσ2, with Re 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 = 120Re(U*/L)1/2. Here, we compare (M/L)N values from this expression to Newtonian inferences for this ratios for the actual (Re, 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.
Abstract Copyright:
© 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Journal keyword(s):
gravitation - stars: kinematics and dynamics - galaxies: kinematics and dynamics - galaxies: structure - galaxies: structure
Simbad objects:
17
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