超微弱dSphs的牛顿M/L比的MONDian预言
MONDian predictions for Newtonian M/L ratios for ultrafaint dSphs
摘要：
在牛顿引力下，dSph星系的总质量将标度为$M_{T} \propto R_{e} σ^{2}$，其中$R_{e}$是有效半径，$σ$是它们的速度色散。当上述两个量都可用时，将得到的质量与观测到的恒星光度进行比较，得出牛顿质量与光的比率，在上面的表达式中给出了物理驱动的比例常数。对于局部dSphs和越来越多的超暗系统样本，上述结果导致了已知任何星系系统中最大的质光比，通常值为数百甚至数千。标准的解释是一种尚未被探测到的暗物质成分占主导地位。然而，如果现实更接近MONDIA理论在极低的加速度相关的系统，$σ$将规模与{恒星质量} $M_{*}^{1/4}$。这就产生了一个在$(M/L)_{N}=120 R_{e}(Υ_{*}/L)^{1/2}$的牛顿假设下得到的质轻比的表达式。在这里，我们比较$(M/L)_{N}$值从这个表达式的牛顿推论，这个比率的实际$(R_{e}, σ, L)$观察值的样品最近观察到的超微弱dSphs，获得良好的协议。然后，对于没有$σ$值的系统，我们给出了预测的$(M/L)_{N}$值下的MONDian计划预计一旦运动学观测变得可用。对于最近研究的Dragonfly 44 {和Crater II系统}，报告的$(M/L)_{N}$值也与MONDian预期值非常一致。
英文摘要：
Under Newtonian gravity total masses for dSph galaxies will scale as $M_{T} \propto R_{e} σ^{2}$, 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, 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 mass to light ratios 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 which will be obtained under Newtonian assumptions of $(M/L)_{N}=120 R_{e}(Υ_{*}/L)^{1/2}$. 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.
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