致命的暗物质尖点与暗淡和扩展的星团：波江座II和仙女座XXV
Deadly dark matter cusps vs faint and extended star clusters: Eridanus II and Andromeda XXV
摘要：
最近在两个本星系群矮星系波江座II和仙女座XXV的中心区域探测到两个暗淡而延伸的星团，这提出了一个问题：具有如此低密度的星团是否能够在具有中心密度尖点的冷暗物质晕的潮汐场中生存下来。使用分析参数和一套无碰撞N体模拟，我表明，这些集群是非常脆弱的，并迅速中断的存在下，中央尖点$ρ\sim r^{-α}$与$α\gtrsim 0.2$。此外，星系团原本质量更大并下沉到晕中心的情况需要非常精细的调整，并且不能自然地重现所观察到的系统。反过来，这些集群长期生活在核心晕中，其中心区域是$α\lesssim 0.2$的安全避难所。唯一可行的情况下，主机已保存其原体尖到目前为止是集群形成在底部的潜力，这是很容易测试的集群内的主机适当的速度测量休息。这提供了一种方法，可以很容易地探测两个像$L_V\sim5\times 10^5 L_\odot$和$L_V\sim6\times10^4 L_\odot$这样微弱的矮星系的中心密度分布，在这两个星系中，恒星反馈不太可能有效。
英文摘要：
The recent detection of two faint and extended star clusters in the central regions of two Local Group dwarf galaxies, Eridanus II and Andromeda XXV, raises the question of whether clusters with such low densities can survive the tidal field of cold dark matter haloes with central density cusps. Using both analytic arguments and a suite of collisionless N-body simulations, I show that these clusters are extremely fragile and quickly disrupted in the presence of central cusps $ρ\sim r^{-α}$ with $α\gtrsim 0.2$. Furthermore, the scenario in which the clusters where originally more massive and sank to the center of the halo requires extreme fine tuning and does not naturally reproduce the observed systems. In turn, these clusters are long lived in cored haloes, whose central regions are safe shelters for $α\lesssim 0.2$. The only viable scenario for hosts that have preserved their primoridal cusp to the present time is that the clusters formed at rest at the bottom of the potential, which is easily tested by measurement of the clusters proper velocity within the host. This offers means to readily probe the central density profile of two dwarf galaxies as faint as $L_V\sim5\times 10^5 L_\odot$ and $L_V\sim6\times10^4 L_\odot$, in which stellar feedback is unlikely to be effective.
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