The First Billion Years

点击翻译按钮获取中文摘要

In the course of my PhD I want to advance the field of what we call "21cm cosmology". Cosmology is the study of the universe on the largest scales and how it evolved over time. 21cm refers to the very weak signal emitted by neutral Hydrogen - this atom can emit or absorb radiation of that wavelength as long as it is not ionized. This happens everywhere in the universe, however the effect is rare and therefore can only be seen when observing large amounts of gas.The early universe (between one million and one billion years of age) is essentially filled with this neutral Hydrogen and we can use the cosmic microwave background, radiation emitted a few hundred thousand years after the big bang, as a flashlight shining through the gas and observe it's absorption or emission behaviour over time.I think much progress can be made by combining methods and information from classical cosmology with the novel observations of the neutral Hydrogen signal. We know very little about the first stars in the universe and a wealth of models has been developed. But using information from the polarization of the cosmic microwave background allows us to limit these possibilities and get a better idea of that time.On the other hand those novel observations can be used to improve our current measurements of the distribution of matter in the universe and the growth of structures with time. We often use galaxies as tracers of the overall distribution of matter in the universe. However they do not paint a complete picture since galaxies only form under certain conditions and we cannot observe the faintest galaxies. Measuring neutral Hydrogen via the 21cm signal gives us a different view and allows us to estimate and correct problems with other methods.Finally this can give us hints or constraints on the nature of Dark Matter as we can probe previously unexplored areas of cosmologies.