Cosmic Dawn and Epoch of Reionization
Cosmic Dawn and Epoch of Reionization with the redshifted 21-cm line
PI: Suman Majumdar
Cosmology is the study of the evolutionary history of our Universe. One of the most important missing pictures in this history is the Cosmic Dawn (CD) and the Epoch of Reionization (EoR), the period during which the very first sources of light were formed and thus marked the end of the dark ages. The radiation emitted by these sources gradually heated and “re”-ionized the neutral and cold hydrogen (HI) in their surrounding inter-galactic medium (IGM). Many fundamental issues regarding this era, such as its timing, duration, and the properties of the sources driving it, are still unresolved. Observations of the redshifted 21-cm signal, emitted by the HI from this era, hold a great promise to resolve many of these puzzles. Several radio telescopes around the world are currently in a race to detect this signal in great detail (for example — GMRT, LOFAR, MWA, PAPER, 21CMA). Very recently, scientists may have got the very first glimpses of this signal through the EDGES experiment. The upcoming enormous Square Kilometre Array (SKA), an international radio telescope of which India is also a member, is expected to be able to image the HI distribution at different cosmic times from the beginning to the end of this era, owing to its great sensitivity. Once the redshifted 21-cm signal from the CD and the EoR is detected, one would require a robust data analysis and interpretation pipeline to answer the unresolved questions regarding this epoch.
My main research interest is focused on the development of such interpretation pipelines. As the actual signal is yet to be detected, such pipelines need to be trained and tested on simulated signal data sets. A major part of my past research focused on the development of detailed but fast computer simulations of the signal, to study different models of reionizations at a relatively low computational cost. Additionally, in the recent past and present, I have been studying different statistical estimators (such as the power spectrum, bispectrum, etc.) of the signal to identify its various unique characteristics, which can be used for the confirmative detection as well as for constraining the different reionization model parameters. As a member of the international Science Working Group for the CD and EoR with the SKA, I am involved in the development of such interpretation tools and pipelines along with my international collaborators. As soon as the SKA becomes operational and starts observing this epoch, it will open up a new exciting phase of cosmological exploration, which will enable us to better understand the Epoch of Reionization. Cosmologists around the world are eagerly waiting for this upcoming new era of “21-cm cosmology” that promises to revolutionize our understanding of the history of the universe.
Simulated redshifts of reionization in three different types of simulations of the EoR (Majumdar et al. 2014).
Quadrupole moments of the redshift space 21-cm power spectrum for different models of reionization (Majumdar et al. 2016).
21-cm bispectrum at three different stages of reionization (Majumdar et al. 2018).