Analysis of di↵erential observations of the cosmological radio background: Studying the SZE-21cm

Abstract

This thesis presents an analytical approach for studying the cosmological 21 cm back ground signal from the Dark Ages (DA) and subsequent Epoch of Reionization (EoR). Di↵erential observations of a galaxy cluster are simulated to demonstrate how these epochs can be studied with a specific form of the Sunyaev-Zel’dovich E↵ect called the SZE-21cm. This work produces the first simulated maps of the SZE-21cm and shows that the SZE-21cm can be extracted from future observations with low-frequency radio interferometers such as the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometre Array (SKA). In order to simulate near realistic scenarios, we look into cosmic variance noise, incorporate and take into account the e↵ects of foregrounds, thermal noise, and angular resolution for our simulated observations. We further extend this exploration by averaging over a sample of galaxy clusters to mitigate the e↵ects of cosmic variance and instrumental noise. Studying the SZE 21cm for di↵erent plasma temperatures, a strategy is proposed to average the signal over multiple clusters of di↵erent plasma temperatures. The impact of point source contamination is also studied. The whole technique is applied to the results of the EDGES collaboration, which in 2018 reported an absorption feature of the global 21 cm background signal centred at 78 MHz. The thesis also investigated the impact of cosmological 21 cm background models on the SZE-21cm, considering cosmologies with Warm Dark Matter, Population II and Population III stellar heating in the early Universe, and excess cooling of the IGM at very high redshift, we find that the SZE 21cm is dependent on global 21 cm signal models and that it can be used to extract the distinct features imprinted on the cosmological signal during DA and EoR by physical processes described in these models. Moreover, di↵erential observations of the SZE-21cm will enable us to rule out any inconsistent models of the global 21 cm signal, and allow for the SZE-21cm to probe the formation and nature of the first sources. Since the di↵erent models for the cosmological 21 cm background provide very similar results, the resulting SZE-21cm signals will also be very similar and it will be challenging to distinguish between them. Our approach demonstrates the po tential of the SZE-21cm as an indirect probe for the DA and EoR, and we conclude that the spectral features of the SZE-21cm from our simulated observations yield results that are close to prior theoretical predictions and that the SZE-21cm can be used to test the validity of the EDGES detection. Early work showed the benefits of the di↵erential analysis technique outside of the SZE-21cm, applying it to observa tions of radio galaxies from the GaLactic and Extra-galactic All-sky MWA survey to enhance features of sources in the continuum images, which can be beneficial for ef forts of source finding, extraction, and characterisation and developing a preliminary pipeline that reduces the e↵ects of contaminating backgrounds and foregrounds