Cosmic Reionization: Galaxy-IGM Physics in the Early Universe

宇宙再电离：早期宇宙中的星系-IGM 物理

• 批准号: ST/K004352/1
• 负责人: George Becker
• 金额: $ 53.3万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2013
• 资助国家: 英国
• 起止时间: 2013 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FK004352%2F1
• 关键词: Cosmic; Reionization; Galaxy; IGM; Physics

The dramatic images of galaxies taken with the Hubble Space Telescope have become familiar symbols of what it "out there" beyond our own Milky Way. What the pictures do not show, however, is that galaxies are only a small part of what fills the Universe. Stretching between galaxies is a vast and invisible network, a "cosmic web" that contains most of the matter in the Universe. This network formed as gravity amplified tiny ripples in the matter created at the Big Bang, and it provides the raw material out of which galaxies form.Galaxies have now been observed back to within one billion years after the Big Bang, when the Universe was less than 7% of its current age. But how and when did the very first galaxies form? Because of the vast distances, most galaxies from this early time are too faint to be observed directly. To learn about the first galaxies, therefore, we must study them through their impact on the cosmic web. We know, for example, that the gas in deep space is highly ionized -- electrons have been stripped from their atoms. We believe that the energy to ionize the gas came from the ultraviolet light emitted by the first stars and galaxies. If we can determine when the gas became ionized, therefore, we will learn when the first galaxies formed.The goal of this proposal is to study the cosmic web far back in time in order to learn about the first galaxies and stars. To do this, I will analyze the way in which the web absorbs light from very luminous objects known as quasars. The gas between a quasar and the Earth absorbs portions of the quasar light in patterns that reveal where the gas is located, its chemical composition, temperature, and ionization state. These quantities, in turn, reflect how the gas has been affected by the galaxies embedded within it.I will first determine when the gas in deep space was ionized by measuring how smoothly it is distributed. As the gas was ionized it would also have been heated to more than 10,000 degrees. The resulting pressure would have caused the gas to expand, smoothing out the smallest bumps in the web. Earlier heating would have produced more smoothing, and so by measuring the smoothness I will be able to determine when the ionization and heating occurred. I will then search for signs of elements made by stars, such as carbon and oxygen. The quantity of these elements in the early Universe will reflect how vigorously stars formed in the first galaxies, and the relative mix of different elements will reveal the nature of the stars themselves. Next, I will determine how efficiently early galaxies produced ionizing photons. By measuring how completely galaxies ionized the gas in the web from one to three billion years after the Big Bang I will will determine how many ultraviolet photons were emitted by all galaxies during this period. A key question will be whether galaxies produced UV photons more efficiently at earlier times, as required if galaxies did indeed drive reionization. Finally, I will investigate the nature of dark matter by analyzing the small-scale structure of the web. This project will determine how "warm" dark matter is, and whether rapidly moving dark matter particles may have inhibited the formation of low-mass galaxies.The emergence of the first galaxies from the cosmic web was a key event in the process that gave rise to galaxies such as our own. Studying the early Universe, therefore, allows us investigate our origins on a grand scale. This field combines cutting-edge technology -- large telescopes and advanced computing -- with basic physics to assemble a picture of the cosmos at the most distant frontier. Ultimately, this research will help us to understand how the early Universe took shape, as well as to explore more of what is "out there."

哈勃太空望远镜拍摄的引人注目的星系图像已经成为我们熟悉的标志，它“在那里”超越了我们自己的银河系。然而，这些照片没有显示的是，星系只是充满宇宙的一小部分。在星系之间延伸的是一个巨大而不可见的网络，一个包含宇宙中大部分物质的“宇宙网”。这个网络是在引力放大了大爆炸时产生的物质中的微小涟漪时形成的，它提供了星系形成的原材料。现在已经观测到星系的存在，可以追溯到大爆炸后的10亿年内，当时宇宙还不到现在年龄的7%。但是第一个星系是如何以及何时形成的呢？由于遥远的距离，早期的大多数星系都太微弱而无法直接观察到。因此，为了了解第一个星系，我们必须通过它们对宇宙网的影响来研究它们。例如，我们知道，深空的气体是高度电离的--电子已经从原子中剥离出来。我们相信，使气体膨胀的能量来自第一批恒星和星系发出的紫外线。如果我们能确定气体是何时被电离的，那么我们就能知道第一个星系是何时形成的。这项计划的目标是研究遥远的宇宙网络，以了解第一个星系和恒星。为了做到这一点，我将分析网络吸收来自被称为类星体的非常明亮的物体的光的方式。类星体和地球之间的气体吸收部分类星体光的模式，揭示了气体的位置，其化学成分，温度和电离状态。这些量，反过来，反映了气体是如何受到嵌在其中的星系的影响的。我将首先通过测量气体分布的平滑程度来确定深空中的气体是何时被电离的。当气体被电离时，它也会被加热到超过10，000度。由此产生的压力会导致气体膨胀，消除网络中最小的凸起。早期的加热会产生更多的平滑，所以通过测量平滑度，我将能够确定电离和加热发生的时间。然后，我将寻找恒星制造的元素的迹象，如碳和氧。这些元素在早期宇宙中的数量将反映出恒星在第一个星系中形成的活跃程度，而不同元素的相对混合将揭示恒星本身的性质。接下来，我将确定早期星系如何有效地产生电离光子。通过测量大爆炸后10亿到30亿年间星系如何完全电离网络中的气体，我将确定在此期间所有星系发射了多少紫外光子。一个关键的问题是，如果星系确实驱动了再电离，那么星系是否在早期更有效地产生紫外光子。最后，我将通过分析网络的小尺度结构来研究暗物质的本质。这个项目将确定暗物质有多“热”，以及快速移动的暗物质粒子是否可能抑制了低质量星系的形成。宇宙网中第一个星系的出现是产生像我们这样的星系的过程中的关键事件。因此，研究早期宇宙可以让我们在更大的范围内研究我们的起源。这个领域结合了尖端技术-大型望远镜和先进的计算-与基础物理学，以在最遥远的前沿组装宇宙的图片。最终，这项研究将帮助我们了解早期宇宙是如何形成的，以及探索更多的“外面”。"

项目成果

A consistent determination of the temperature of the intergalactic medium at redshift (z) = 2.4

一致确定红移 (z) = 2.4 时星系间介质的温度

• DOI: 10.17863/cam.26861
• 发表时间: 2014
• 作者: Bolton J

New constraints on the free-streaming of warm dark matter from intermediate and small scale Lyman-a forest data

中小尺度莱曼森林数据中暖暗物质自由流动的新限制

• DOI: 10.17863/cam.28062
• 发表时间: 2017
• 作者: IRSIC V

Testing metallicity indicators at z ~ 1.4 with the gravitationally lensed galaxy CASSOWARY 20?

使用引力透镜星系 CASSOWARY 20 测试 z ~ 1.4 处的金属丰度指标？

• DOI: 10.1093/mnras/stu287
• 发表时间: 2014
• 期刊: Monthly Notices of the Royal Astronomical Society
• 影响因子: 4.8
• 作者: James B

New Measurements of the Ionizing Ultraviolet Background over 2 < z < 5 and Implications for Hydrogen Reionization

• DOI: 10.1093/mnras/stt1610
• 发表时间: 2013-07
• 期刊: Monthly Notices of the Royal Astronomical Society
• 影响因子: 4.8
• 作者: G. Becker;J. Bolton

First Constraints on Fuzzy Dark Matter from Lyman-a Forest Data and Hydrodynamical Simulations.

来自莱曼森林数据和流体动力学模拟的模糊暗物质的第一约束。

• DOI: 10.17863/cam.26837
• 发表时间: 2017
• 作者: Iršic V