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An Illumination of the Dark Ages: modeling reionization and interpreting observations

Periodic Reporting for period 3 - AIDA (An Illumination of the Dark Ages: modeling reionization and interpreting observations)

Reporting period: 2018-05-01 to 2019-10-31

The goal of AIDA is to investigate the birth of the very first stars and galaxies in our Universe, occurring over 13 billion years ago. These galaxies are too faint to be seen directly, even with the most advanced telescopes. Yet their light heated and ionized virtually every atom in the Universe, in an important milestone called Cosmic Reionization. We are developing state-of-the-art simulations and statistically comparing them to observations. In doing so, we will quantify what can we learn about the first galaxies from the timings and patterns of Cosmic Reionization. Ultimately, AIDA will help us understand the mysterious origins of the structures of our Universe.
During this reporting period, we focused on analyzing the spectra of quasars present during the first billion years of our Universe. Quasars, powered by accretion onto massive black holes, are among the brightest objects in our Universe. Their light can be used to probe the intervening matter as it travels to us. We developed a state-of-the-art analysis, which combined data from over a thousand relatively nearby quasars, in order to predict what the intrinsic spectra of these objects should be. Using this prediction of the intrinsic spectra of a z=7.1 bright quasar, we were able to compute how much of the light was absorbed by matter along the way to us.

The other main focus of our efforts was how to make sense of upcoming cosmic 21cm observations. Powerful radio telescopes are set to 'image' the Epoch of Reionization and the Cosmic Dawn. The patters they will discover will tell us about the nature of the very first galaxies. We created the theoretical framework which will quantify this insight. We made forecasts showing how these telescopes will nail down important physical properties of the first structures, to orders of magnitude better precision that is available with today's observations.
Our results are far beyond the state of the art. Thus far, our work resulted in: (i) the only model-independent constraint on reionization using dark-fraction statistics form high redshift quasars; (ii) the first ever detection of on-going reionization from the spectrum of a z=7.1 QSO; (iii) the first ever Bayesian parameter estimates for upcoming 21-cm observations. Our work on interpreting the cosmic 21cm signal is part of the official analysis pipelines for both next generation radio interferometers, HERA and SKA.

Our results were published in peer-reviewed journals, and all work was made immediately available on the arXiv pre-print server. The codes we developed and improved, 21cmFAST and 21CMMC, are publicly available on the github repository. These codes are used by researchers in over 17 countries around the globe.
Slice through a cosmological simulation of the 21cm radio signal.