WHERE ARE THE FOSSILS OF THE FIRST GALAXIES? II. TRUE FOSSILS, GHOST HALOS, AND THE MISSING BRIGHT SATELLITES
WHERE ARE THE FOSSILS OF THE FIRST GALAXIES? II. TRUE FOSSILS, GHOST HALOS, AND THE MISSING BRIGHT SATELLITES
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第一个星系的化石在哪里？
DOI：
10.1088/0004-637x/741/1/18
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
M. Ricotti
中科院分区：
文献类型：
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作者：
M. Bovill;M. Ricotti
我们使用一套新的冷暗物质模拟局部宇宙来研究银河系内部和周围原始矮星系化石的分布。在整个过程中，我们建立在先前的结果的基础上，这些结果显示了超微弱矮星子集的恒星特性与我们的模拟化石之间的一致性。在这里，我们证明了第一批星系的化石具有与观测一致的星系中心分布和累积光度函数。在我们的模型中，我们预测大约有300颗围绕银河系运行的发光卫星，其中50%-70%是保存完好的化石。在银河系的恒星半径内，这些化石的光度大多小于106 L☉。尽管我们在多维度上与低质量和低光度的观测一致，原始模型产生了大量的亮矮卫星（LV > 104 L☉），相对于观测几乎完成的观测。“明亮的卫星问题”在银河系的外围最为明显。我们估计，虽然相对明亮，但原始恒星群非常分散，产生了表面亮度低于调查检测极限的恒星群，并且很容易被潮汐力剥离。虽然我们还不能提供本星系群中第一批星系化石存在的确凿证据，但我们的研究结果提出了可能证明它们存在的观测策略：(1)探测到孤立矮星周围原始恒星的“鬼晕”将证明恒星在再电离之前形成于微晕（M < 108 M☉），并强烈表明至少有一部分超暗矮星是第一批星系的化石；(2)存在一个未知的约150个银河系超暗星系群，它们的半光半径rhl≈100 - 1000pc，光度LV < 104 L☉，可以被未来的深度观测探测到。这些未被探测到的矮星将具有本研究预测的质量与光比、恒星速度色散和金属丰度。
We use a new set of cold dark matter simulations of the local universe to investigate the distribution of fossils of primordial dwarf galaxies within and around the Milky Way. Throughout, we build upon previous results showing agreement between the observed stellar properties of a subset of the ultra-faint dwarfs and our simulated fossils. Here, we show that fossils of the first galaxies have galactocentric distributions and cumulative luminosity functions consistent with observations. In our model, we predict ∼300 luminous satellites orbiting the Milky Way, 50%–70% of which are well-preserved fossils. Within the Milky Way virial radius, the majority of these fossils have luminosities LV < 106 L☉. Despite our multidimensional agreement with observations at low masses and luminosities, the primordial model produces an overabundance of bright dwarf satellites (LV > 104 L☉) with respect to observations where observations are nearly complete. The “bright satellite problem” is most evident in the outer parts of the Milky Way. We estimate that, although relatively bright, the primordial stellar populations are very diffuse, producing a population with surface brightnesses below surveys’ detection limits, and are easily stripped by tidal forces. Although we cannot yet present unmistakable evidence for the existence of the fossils of first galaxies in the Local Group, the results of our studies suggest observational strategies that may demonstrate their existence: (1) the detection of “ghost halos” of primordial stars around isolated dwarfs would prove that stars formed in minihalos (M < 108 M☉) before reionization and strongly suggest that at least a fraction of the ultra-faint dwarfs are fossils of the first galaxies; and (2) the existence of a yet unknown population of ∼150 Milky Way ultra-faints with half-light radii rhl ≈ 100–1000 pc and luminosities LV < 104 L☉, detectable by future deep surveys. These undetected dwarfs would have the mass-to-light ratios, stellar velocity dispersions, and metallicities predicted in this work.