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arXiv 1802.10096astro-ph.GAastro-ph.CO
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宇宙再电离对星系光度函数的影响

The imprint of cosmic reionisation on the luminosity function of galaxies

Sownak Bose, Alis J. Deason, Carlos S. Frenk

摘要:

早期宇宙中氢的(再)电离对第一个星系的形成有着深远的影响:通过提高气体的温度和压力,它阻止了气体冷却成小晕,从而影响了今天小星系的丰度。使用Galform半解析模型的星系形成,我们表明,两个关键方面的再电离过程-当再电离发生和特征尺度低于它抑制星系形成-是印在矮星系的光度函数。我们专注于像银河系和大麦哲伦星系的卫星的光度函数,这是更容易测量比作为一个整体的矮人口的光度函数。我们的研究结果表明,再电离的这两个特性的细节确定的形状的光度分布的卫星以一种独特的方式,在很大程度上是独立的星系形成模型的其他细节。我们的模型一般预测双峰分布的卫星作为光度的函数:人口的微弱卫星和人口的明亮卫星分离的“山谷”伪造的再电离。我们发现,这种双峰分布是目前在银河系和M31的组合卫星光度函数的统计意义。我们对LMC质量矮星周围的预期卫星数量进行预测,在未来的观测计划中,双峰也可能是可测量的。我们的首选模型预测的$26 \pm 10$(68%的置信度)卫星比LMC质量系统中的${\rm M}_V=0$亮。

英文摘要:

The (re)ionisation of hydrogen in the early universe has a profound effect on the formation of the first galaxies: by raising the gas temperature and pressure, it prevents gas from cooling into small haloes thus affecting the abundance of present-day small galaxies. Using the Galform semi-analytic model of galaxy formation, we show that two key aspects of the reionisation process -- when reionisation takes place and the characteristic scale below which it suppresses galaxy formation -- are imprinted in the luminosity function of dwarf galaxies. We focus on the luminosity function of satellites of galaxies like the Milky Way and the LMC, which is easier to measure than the luminosity function of the dwarf population as a whole. Our results show that the details of these two characteristic properties of reionisation determine the shape of the luminosity distribution of satellites in a unique way, and is largely independent of the other details of the galaxy formation model. Our models generically predict a bimodality in the distribution of satellites as a function of luminosity: a population of faint satellites and population of bright satellites separated by a 'valley' forged by reionisation. We show that this bimodal distribution is present at high statistical significance in the combined satellite luminosity function of the Milky Way and M31. We make predictions for the expected number of satellites around LMC-mass dwarfs where the bimodality may also be measurable in future observational programmes. Our preferred model predicts a total of $26 \pm 10$ (68 per cent confidence) satellites brighter than ${\rm M}_V=0$ in LMC-mass systems.

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