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

Periodic Reporting for period 4 - AIDA (An Illumination of the Dark Ages: modeling reionization and interpreting observations)

Reporting period: 2019-11-01 to 2021-04-30

The AIDA project investigated 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. Within AIDA we developed state-of-the-art simulations and statistically compared them to observations. In doing so, we quantified what can we learn about the unseen first galaxies from the timings and patterns of Cosmic Reionization.

Our work resulted in: (i) the first ever detection of on-going reionization from the spectrum of a redshift 7 quasar; (ii) the first ever Bayesian parameter estimates for current observations and upcoming cosmic 21-cm observations; (iii) 21cmMC - a public code capable of forward modeling full 4D realizations of the first billion years of our Universe. The tools we developed are being used to interpret the data from all cosmic 21-cm telescopes. Ultimately with the advent of upcoming data from the Square Kilometer Array (SKA), AIDA will help us understand the mysterious origins of the structures of our Universe.
In AIDA we analyzed 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. This resulted in the first ever detection of on-going cosmic reionization.

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. They will map out the majority of the visible volume of our Universe, driving a data-rich revolution in astrophysics and cosmology. The patterns they discover will tell us about the nature of the very first galaxies. We created the theoretical framework which will be used to interpret these upcoming observations. We made forecasts showing how these telescopes will nail down important physical properties of the first galaxies, to orders of magnitude better precision than is available with today's observations. Our code is public on github and is used by all of the relevant telescopes.

Our results were published in peer-reviewed journals, and all work was made immediately available on the arXiv pre-print server. Our team presented the results in many international conferences and workshops. The codes we developed and improved, 21cmFAST and 21cmMC, are publicly available on the github repository. These codes are used by independent researchers in over 25 countries around the globe.
Our results are far beyond the state of the art. Our work resulted in: (i) the first ever detection of on-going reionization from the spectrum of a z=7.1 QSO; (ii) the first ever Bayesian parameter estimates for current observations and upcoming 21-cm observations; (iii) 21cmMC - a public code capable of forward modeling full 4D realizations of the first billion years of our Universe. Our work on interpreting the cosmic 21cm signal is part of the official analysis pipelines for both next generation radio interferometers, HERA and SKA.
Slice through a cosmological simulation of the 21cm radio signal.