COSMICDAWN21CM · Probing the cosmic dawn and the epoch of reionization with the history and fluctuations of the hydrogen 21-cm line

One of the frontiers being explored by astronomy today is theperiod between approximately 400000 years after the Big Bang, fromwhich time we can detect the cosmic microwave background (CMB)radiation, and around one billion years after the Big Bang, whenearly galaxies and quasars start to become visible to currentinstruments, such as ALMA and the Wide Field Camera 3 on HST. Themost promising observational probe of this period is the redshifted21-cm hyperfine line of atomic hydrogen.The LOFAR telescope is now operational, and from its site in theNetherlands will be able to detect 21-cm radiation from the latterpart of this period, the 'epoch of reionization' (EoR). Foregroundradiation at the same frequency is several orders of magnitude moreintense than the cosmological signal, however. Moreover, the datawill have low signal-to-noise and be filtered through a complexinstrument. As one of the core members of the LOFAR EoR keyproject, I have developed techniques to extract information aboutcosmology and reionization from the data, and applied them tosynthetic EoR observations. During the fellowship, I will continueto develop and extend these methods with the help of the expertisein data analysis and novel statistical methods at UCL, begin toapply them to the real data which will start to arrive during theperiod of the fellowship, and use them to learn about the EoR.Other experiments are being proposed which would be able to probeearlier parts of this period, the 'dark ages' and the 'cosmicdawn'. I am a co-investigator on a satellite mission, the Dark AgesRadio Explorer (DARE), which will be proposed to NASA's 2013Explorer program. It would take a complementary approach toLOFAR's, observing the sky-averaged 21-cm signal (rather than itsfluctuations) at even lower radio frequencies, with the aim oflearning about the very first stars and black holes. Analysing itsdata presents a different challenge, and will also require noveltechniques.