论文标题
仙女座XXV-中央暗物质密度低的矮星系
Andromeda XXV -- a dwarf galaxy with a low central dark matter density
论文作者
论文摘要
以前曾报道过仙女座（和）XXV，是矮球星系（DSPH），几乎没有暗物质。但是，对此结果的不确定性很大。在这项研究中，我们将成员恒星的数量和XXV的运动学和质量重新衍生。我们发现，XXV的系统性速度为$ν_\ Mathrm {r} = - 107.7 \ pm1.0 \ pm1.0 \ Mathrm {〜km s}^{ - 1} $和$σ_ν= 4.5 \ pm1.0 \ pm1.0 \ pm1.0 \ mathrm {通过这种更好约束的速度分散，我们得出了$ m（r <r_ \ m atrm {h}）= 6.9^{+3.2} _ { - 2.8} \ times10^6 \ m mathrm {〜m} _ \ odot $。该质量对应于$ \ mathrm {[m/l]} _ \ mathrm {r_ \ mathrm {h}} = 37^{+17} _ { - 15} \ Mathrm {〜Mathrm {〜M MATHRM {〜M MATHRM {〜M MATHRM {具有明确的暗物质组件。我们还测量的金属性和XXV的金属性为$ \ MATHRM {[Fe/H]} = - 1.9 \ PM0.1 $$ \ MATHRM {〜} $ DEX，与先前的结果一致。最后，我们将分析和XXV的分析扩展到使用Gravsphere的质量建模。我们发现，XXV的中央暗物质密度低，$ρ_\ MATHRM {dm}（150 \ Mathrm {pc}）= 2.7^{+1.8} _ { - 1.6} \ times10^7 \ times10^7 \ Mathrm {〜M Mathrm {〜M} _ \ odot \ odot \ odot \ odot \ mathrm {与类似恒星质量的其他本地组（LG）DSPH相比，离群值更高。在同伴论文中，我们将探讨暗物质尖核转换和/或潮汐的某种组合是否可以解释以及XXV的低密度。
Andromeda (And) XXV has previously been reported as a dwarf spheroidal galaxy (dSph) with little-to-no dark matter. However, the uncertainties on this result were significant. In this study, we double the number of member stars and re-derive the kinematics and mass of And XXV. We find that And XXV has a systemic velocity of $ν_\mathrm{r}=-107.7\pm1.0 \mathrm{~km s}^{-1}$ and a velocity dispersion of $σ_ν=4.5\pm1.0\mathrm{~km s}^{-1}$. With this better constrained velocity dispersion, we derive a mass contained within the half-light radius of $M(r< r_\mathrm{h})=6.9^{+3.2}_{-2.8}\times10^6\mathrm{~M}_\odot$. This mass corresponds to a mass-to-light ratio of $\mathrm{[M/L]}_\mathrm{r_\mathrm{h}}=37^{+17}_{-15}\mathrm{~M}_\odot/\mathrm{L}_\odot$, demonstrating, for the first time, that And XXV has an unambiguous dark matter component. We also measure the metallicity of And XXV to be $\mathrm{[Fe/H]}=-1.9\pm0.1$$\mathrm{~}$dex, which is in agreement with previous results. Finally, we extend the analysis of And XXV to include mass modelling using GravSphere. We find that And XXV has a low central dark matter density, $ρ_\mathrm{DM}(150\mathrm{pc})= 2.7^{+1.8}_{-1.6}\times10^7\mathrm{~M}_\odot\mathrm{kpc}^{-3}$, making And XXV a clear outlier when compared to other Local Group (LG) dSphs of the similar stellar mass. In a companion paper, we will explore whether some combination of dark matter cusp-core transformations and/or tides can explain And XXV's low density.
