Special Astrophysics Seminar

The 21-cm line as a new probe of magnetic fields in the pre-reionization epoch

Teja Venumadhav

Caltech

Mapping neutral hydrogen using the 21cm line is one of the next big observational frontiers in cosmology. Its main advantage is that it provides redshift information, and enables access to many more modes than the CMB does. I will highlight another feature of the line which makes it possible to extract even more interesting cosmological information from high-resolution 21cm observations, when they are realized in the future. This is the spin-degeneracy of the triplet excited state of the transition, which is spin-polarized by anisotropies in the incident radiation. In this talk, I will focus on fluctuations in the brightness temperature seen by a present-day observer, and show that they encode information about magnetic fields which are coherent on large scales in the early universe. This technique will be naturally sensitive to extremely weak field strengths of order 10^-19 G, which opens the possibility of probing primordial magnetic fields in neutral gas prior to reionization. I will also briefly touch upon the exciting, if even more speculative possibility of studying tensor modes using the 21cm line.