Date of Award
Doctor of Philosophy (PhD)
Astrophysical & Planetary Sciences
Jack O. Burns
J. Michael Shull
Vanja M. Dukic
Steven R. Furlanetto
Within the first billion years after the Big Bang, the intergalactic medium (IGM) underwent a remarkable transformation, from a uniform sea of cold neutral hydrogen gas to a fully ionized, metal-enriched plasma. Three milestones during this Epoch of Reionization – the emergence of the first stars, black holes, and full-fledged galaxies – are expected to manifest as spectral “turning points” in the sky-averaged (“global”) 21-cm background. However, interpreting these measurements will be complicated by the presence of strong foregrounds and non-trivialities in the radiative transfer (RT) required to model the signal.
In this thesis, I make the first attempt to build the final piece of a global 21-cm data analysis pipeline: an inference tool capable of extracting the properties of the IGM and the Universe’s first galaxies from the recovered signal. Such a framework is valuable even prior to a detection of the global 21-cm signal as it enables end-to-end simulations of 21-cm observations that can be used to optimize the design of upcoming instruments, their observing strategies, and their signal extraction algorithms.
En route to a complete pipeline, I found that (1) robust limits on the physical properties of the IGM, such as its temperature and ionization state, can be derived analytically from the 21-cm turning points within two-zone models for the IGM, (2) improved constraints on the IGM properties can be obtained through simultaneous fitting of the global 21-cm signal and foregrounds, though biases can emerge depending on the parameterized form of the signal one adopts, (3) a simple four-parameter galaxy formation model can be constrained in only 100 hours of integration provided a stable instrumental response over a broad frequency range (~80 MHz), and (4) frequency-dependent RT solutions in physical models for the global 21-cm signal will be required to properly interpret the 21-cm absorption minimum, as the IGM thermal history is highly sensitive to the spectral energy distribution of the first galaxies. These results highlight the need for continued development of theoretical models that can incorporate constraints from current and near-future observatories, and the implementation of statistical algorithms capable of distinguishing competing models.
Mirocha, Jordan, "From Darkness to Light: Signatures of the Universe's First Galaxies in the Cosmic 21-cm Background" (2015). Astrophysical & Planetary Sciences Graduate Theses & Dissertations. 37.