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arXiv 2106.09050astro-ph.GA
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Milky Way卫星速度函数是研究小尺度结构问题的一个很好的工具

The Milky Way satellite velocity function is a sharp probe of small-scale structure problems

Stacy Y. Kim, Annika H. G. Peter

摘要:

20年前,观测到的银河系卫星星系数量与预测的冷暗物质(CDM)暗晕数量之间的不匹配被称为"卫星失踪问题"。虽然大多数情况下是在光度空间中的卫星计数方面,但失踪卫星问题最初是在速度空间中提出的。重要的是,恒星速度色散函数编码了卫星密度分布及其丰度的信息。在这项工作中,我们完全正确的MW卫星恒星速度色散函数下降到超微弱的矮星($L \gtrsim 340$ L $_\odot$)。我们最保守的完整性修正是在一个简单的CDM模型,其中大规模的,经典的卫星(M $_{\rm 200} \gtrsim 5 \times 10^8~$ M $_\odot$)重子驱动的核心,而较低的质量,超微弱的卫星居住的尖状晕没有强烈的潮汐剥离。MW圆盘对卫星的潮汐破坏必须是最小的,否则完整性校正的速度函数超过任何合理的CDM预测-一个"太多卫星"的问题。我们排除了非核心坍缩的自相互作用暗物质模型与恒定的横截面$\gtrsim$ 0.1 cm $^2$/g。对暖暗物质的约束比基于光度函数的约束更强,这是因为它对晕下中心密度的额外敏感性,从而抑制了额外30%的数量计数。热残余质量$\gtrsim$ 6 keV是优选的。减少恒星速度色散测量的不确定性和最暗的矮星所经历的潮汐剥离量是确定卫星太多问题严重性的关键。

英文摘要:

Twenty years ago, the mismatch between the observed number of Milky Way satellite galaxies and the predicted number of cold dark matter (CDM) subhalos was dubbed the ``missing satellites problem". Although mostly framed since in terms of satellite counts in luminosity space, the missing satellites problem was originally posed in velocity space. Importantly, the stellar velocity dispersion function encodes information about the density profile of satellites as well as their abundance. In this work, we completeness correct the MW satellite stellar velocity dispersion function down to its ultrafaint dwarfs ($L \gtrsim 340$ L$_\odot$). Our most conservative completeness correction is in good agreement with a simple CDM model in which massive, classical satellites (M$_{\rm 200} \gtrsim 5 \times 10^8~$M$_\odot$) have baryon-driven cores, while lower mass, ultrafaint satellites inhabit cuspy halos that are not strongly tidally stripped. Tidal destruction of satellites by the MW's disk must be minimal, otherwise the completeness-corrected velocity function exceeds any plausible CDM prediction -- a ``too many satellites" problem. We rule out non-core-collapsing self-interacting dark matter models with a constant cross section $\gtrsim$ 0.1 cm$^2$/g. Constraints on warm dark matter are stronger than those based on the luminosity function due to its additional sensitivity to subhalo central densities, which suppresses number counts by up to an additional 30%. A thermal relic mass $\gtrsim$ 6 keV is preferred. Reducing uncertainties on stellar velocity dispersion measurements and the amount of tidal stripping experienced by the faintest dwarfs is key to determining the severity of the too many satellites problem.

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