Katherine Mack (Cambridge University)

The 21cm Forest: High-Redshift Radio Sources as Probes of Reionization

Future observations of the 21cm forest -- neutral hydrogen absorption against high-redshift radio sources -- will allow us to trace out the structure of the pre-reionization intergalactic medium (IGM), provided bright radio sources can be found at sufficiently high redshift. I will present a calculation of the expected 21cm forest as might be observed in coming years and show how statistical detection techniques could be used to overcome the low signal-to-noise. I will also discuss the trade-off between the availability of large populations of high-redshift background radio sources and the requirement that the IGM be sufficiently neutral for strong absorption. (http://arxiv.org/abs/1101.5431)

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Thomas Greif (MPA Garching)

The Formation of the First Stars

I will discuss the formation of the first stars, which transformed the Universe from its simple initial state to one of ever increasing complexity. The utilization of novel simulation techniques have helped to advance our theoretical understanding of their formation and led to exciting results, in particular concerning the fragmentation of primordial gas and the early termination of accretion by radiation feedback. I will further discuss the effects of supersonic streaming velocities between baryons and dark matter on the formation of the first stars - an important issue that was overlooked in linear perturbation theory.