Description
- Abstract:
- From the release of the CMB at redshift z ~ 1100, when the CMB was released, to around z ~ 6, where the most distant quasars are observed, lies an unobserved stretch of cosmic history. During this time, the first large scale structures grew from small perturbations, the first stars ignited, and early galaxies emitted UV radiation which re-ionized the intergalactic medium (IGM) into the fully ionized universe we see today. This last stage, when these luminous sources heated and ionized the universe, is known as the Epoch of Reionization (EoR). The 21 cm hyperfine transition of neutral hydrogen (HI) offers a window into this period, as it can be used to directly map the three-dimensional structure of the IGM throughout cosmic history. Experiments to measure this signal must contend with foreground contaminants 5 orders of magnitude brighter than the expected signal. Though bright, these foregrounds have very smooth spectra, which allows their power to be isolated from the EoR signal in Fourier space provided the observing instrument does not introduce any spectral structure. Understanding and mitigating these sources of spectral structure has been an ongoing effort. Precise and detailed simulations of the instrument response have revealed several effects that were unknown in radio astronomy, but relevant to the challenge of 21 cm detection. Previous generations of simulators have lacked sufficient standards of verification, and made it impossible to determine whether some observed artifacts were due to the simulation architecture or realistic to the instrument. In this work, I present two new instrument simulation tools. The simulator pyuvsim has been collaboratively written within a robust test framework to provide the most precise and accurate simulated visibilities available, and has come to serve as a reference standard within the HERA collaboration. In addition, I have written a new diffuse simulator called healvis which has been validated against pyuvsim and analytic calculations. With healvis simulations, I have studied the time-correlation properties of drift-scan observations of EoR-like signals and measured the sample variance of realistic observations of such signals, as a fundamental lower limit on the precision that can be obtained from current experiments. In addition, I have looked at the impact of various instrumental effects on the spread of diffuse foreground power in Fourier space, testing the limits of what Fourier modes can be detected.
- Notes:
- Thesis (Ph. D.)--Brown University, 2019
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Citation
Lanman, Adam Eudene,
"Precision Simulation of Low-Frequency Radio Interferometers"
(2019).
Physics Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://repository.library.brown.edu/studio/item/bdr:1129452/
