Galactic Cosmology: Dark Matter and the Faint End of Galaxy Formation

银河宇宙学：暗物质和星系形成的微弱尽头

• 批准号: RGPIN-2019-04172
• 负责人: Navarro, Julio
• 金额: $ 4.44万
• 依托单位: University of Victoria
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=763056
• 关键词: Galactic; Cosmology; Dark; Matter; Faint

Our understanding of Cosmology rests on two fundamental puzzles-"dark matter" and "dark energy"- whose solution will redefine the way we understand Physics. The nature of dark matter, in particular, is key to extending the Standard Model of Particle Physics and to understanding the hierarchical nature of structure formation in the Universe. Studies of the Cosmic Microwave Background radiation and of galaxy clustering have led to a true paradigm, where dark matter takes the form of weakly-interacting elementary particles that emerge from the early Universe with negligible thermal velocities. This Lambda-Cold-Dark-Matter (LCDM) scenario has now matured into a full, falsifiable theory where detailed theoretical predictions may be directly confronted with observation and experiment. A cornerstone prediction of LCDM is that dark matter halos (non-linear structures where galaxies form) exist in vast numbers and span a very large range in mass. The mass function of LCDM halos, however, differs markedly from the galaxy mass function: galaxy masses and halo masses must thus be related by a strongly non-linear function that contains signatures of the astrophysical processes that govern galaxy formation. This relation has particularly intriguing consequences in the regime of faint (dwarf) galaxies. Since low-mass halos vastly outnumber dwarfs, reconciling LCDM with observation requires that luminous galaxies have only been able to form in a small fraction of low-mass halos. Most low-mass halos must thus be "dark", and dwarf galaxy formation must effectively be cut off below a characteristic halo mass of order ~109 solar masses. This "threshold" halo mass should leave clear observational imprints in the faintest dwarfs which, if properly elucidated, could serve to validate or falsify some of the basic tenets of the cold dark matter paradigm. One example are halos just below the threshold, which, although unable to form stars, should still retain part of their primordial gas content. Detecting this population of gas-filled, star-less "mini-halos" filled would be a major discovery and a resounding success for LCDM on small scales. The faintest dwarfs are best studied in the Local Group of Galaxies, since they can only be detected out to a few Mpc. Some dwarfs, in addition, may have melded into the Galaxy at early times, leaving clues to their origin in the kinematics, metallicities, and abundance patterns of Galactic stars. I propose an ambitious plan to turn the Milky Way (the "Galaxy") into a powerful cosmological probe, combining supercomputer simulations, data mining, and direct observational surveys to decipher the cosmological clues buried in the Galaxy and its immediate neighbours. The aim of this "Galactic Cosmology" is to learn how to use the faintest, and most puzzling, specimens of the galaxy population to pry open a unique astronomical window into one of the defining Physics challenges of our era-the nature of dark matter.

我们对宇宙学的理解基于两个基本难题——“暗物质”和“暗能量”——它们的解决方案将重新定义我们理解物理学的方式。特别是暗物质的性质是扩展粒子物理标准模型和理解宇宙结构形成的层次性质的关键。对宇宙微波背景辐射和星系团聚的研究已经产生了一个真正的范例，其中暗物质采取弱相互作用的基本粒子的形式，这些粒子以可忽略的热速度从早期宇宙中出现。这种 Lambda 冷暗物质 (LCDM) 场景现已成熟为一个完整的、可证伪的理论，其中详细的理论预测可以直接面对观察和实验。 LCDM 的一个基石预测是暗物质晕（星系形成的非线性结构）大量存在并且质量范围非常大。然而，LCDM 晕的质量函数与星系质量函数明显不同：因此，星系质量和晕质量必须通过一个强非线性函数关联起来，该函数包含控制星系形成的天体物理过程的特征。这种关系在微弱（矮）星系的体系中具有特别有趣的后果。由于低质量晕的数量远远多于矮星，因此要使 LCDM 与观测相一致，就需要发光星系只能在低质量晕的一小部分中形成。因此，大多数低质量晕必须是“暗”的，并且矮星系的形成必须有效地被切断，低于大约 109 个太阳质量的特征晕质量。这个“阈值”晕质量应该在最微弱的矮星中留下清晰的观测印记，如果得到适当的阐明，可以用来验证或证伪冷暗物质范式的一些基本原则。一个例子是略低于阈值的光晕，虽然无法形成恒星，但仍应保留部分原始气体含量。探测到这些充满气体、无恒星的“迷你光环”将是一项重大发现，也是小尺度 LCDM 的巨大成功。 最微弱的矮星最好在本星系群中进行研究，因为它们只能在几个 Mpc 范围内被探测到。此外，一些矮星可能在早期就融入了银河系，在银河系恒星的运动学、金属丰度和丰度模式中留下了它们起源的线索。我提出了一项雄心勃勃的计划，将银河系（“银河系”）变成一个强大的宇宙学探测器，结合超级计算机模拟、数据挖掘和直接观测调查来破译埋藏在银河系及其近邻中的宇宙学线索。 “银河宇宙学”的目的是学习如何利用星系群中最微弱、最令人费解的样本，撬开一扇独特的天文学窗口，了解我们这个时代的决定性物理学挑战之一——暗物质的本质。