Role of CMB In constraining the era of reionization

The epoch of reionization marked the last major phase change in the ionization state of the universe. This period is linked with birth of the first luminous sources in history which ionized the previously neutral Intergalactic medium (IGM). The nature of these sources and the timeline of reionization are still open questions in cosmology.

While much of reionization remains hidden from view, the Cosmic Microwave Background photons (CMB) is one of the most powerful ways to probe this remote epoch. In particular, secondary anisotropies in CMB temperature and polarization carry signatures of reionization as the traversing CMB photons get Thomson scattered from the free electron population in the ionized IGM.  With recent (SPT, BICEP2) and upcoming advancements in CMB observations (Simon’s Observatory,CMB-S4, LiteBIRD and more) in terms of detector sensitivity and survey area, detection of these secondary anisotropies is expected. In addition to their role as probe of reionization, proper understanding of these anisotropies will give us a chance to retrieve any buried signatures from before the last scattering era especially the much anticipated signatures of primordial gravitational waves in the B mode polarization of CMB.

My interest primarily lies in accurate modelling of these signatures on CMB to further our understanding about the era of reionization.