Detecting Galaxies in the Epoch of Reionization

Magister Scientiae - MSc (Physics)The aim of this project was to develop a technique that allows us to measure the redshift of radio galaxies in the Epoch of Reionization. We achieved this by constructing a parameterization of the 21-cm absorption feature which is expected to be seen in the spectra of high redshift radio galaxies. A Bayesian framework for parameter estimation and model selection was applied on the candidate models found. The method's proficiency is demonstrated with two data sets: SIMFAST21-generated & model-generated data. The SIMFAST21-generated data was constructed using a simulation of the Epoch of Reionization. The model-generated data was synthesized from our best analytical model for the 21-cm absorption feature. A spectrum template from radio galaxies at low redshifts was then combined with the data sets. The resulting spectra are fitted using a model that accounts for 21-cm absorption feature. The parameter fitting was done using the expected SKA1-LOW noise. A strong detection can be achieved for galaxies with redshifts zg >12 and luminosities L > 1026[W/Hz]. Objects at lower z, although with brighter flux, are harder to detect due to the weak absorption feature (e.g. less intervening HI). A detection proxy grid space was assembled to quantify model evidence found when fitting data with the best model and null hypothesis (no absorption). To interpret the detection proxy, the Jeffreys scale was used. The grid for both data sets was overlaid with the SKADS simulated sources. In a 25 deg2 sky area, a total of 62206 "SKADS" radio galaxies above redshift 7 are expected to be detected in continuum by SKA-LOW. From these, about 1% should be confirmed to be in the epoch of reionization by SKA-LOW (with the same survey) through the detection of the 21 cm absorption feature using the proposed techniqu

Detection of Cosmic Structures using the Bispectrum Phase. II. First Results from Application to Cosmic Reionization Using the Hydrogen Epoch of Reionization Array

Characterizing the epoch of reionization (EoR) at $z\gtrsim 6$ via the redshifted 21 cm line of neutral Hydrogen (HI) is critical to modern astrophysics and cosmology, and thus a key science goal of many current and planned low-frequency radio telescopes. The primary challenge to detecting this signal is the overwhelmingly bright foreground emission at these frequencies, placing stringent requirements on the knowledge of the instruments and inaccuracies in analyses. Results from these experiments have largely been limited not by thermal sensitivity but by systematics, particularly caused by the inability to calibrate the instrument to high accuracy. The interferometric bispectrum phase is immune to antenna-based calibration and errors therein, and presents an independent alternative to detect the EoR HI fluctuations while largely avoiding calibration systematics. Here, we provide a demonstration of this technique on a subset of data from the Hydrogen Epoch of Reionization Array (HERA) to place approximate constraints on the brightness temperature of the intergalactic medium (IGM). From this limited data, at $z=7.7$ we infer "$1\sigma$" upper limits on the IGM brightness temperature to be $\le 316$ "pseudo" mK at $\kappa_\parallel=0.33$ "pseudo" $h$ Mpc$^{-1}$ (data-limited) and $\le 1000$ "pseudo" mK at $\kappa_\parallel=0.875$ "pseudo" $h$ Mpc$^{-1}$ (noise-limited). The "pseudo" units denote only an approximate and not an exact correspondence to the actual distance scales and brightness temperatures. By propagating models in parallel to the data analysis, we confirm that the dynamic range required to separate the cosmic HI signal from the foregrounds is similar to that in standard approaches, and the power spectrum of the bispectrum phase is still data-limited (at $\gtrsim 10^6$ dynamic range) indicating scope for further improvement in sensitivity as the array build-out continues.Comment: 22 pages, 12 figures (including sub-figures). Published in PhRvD. Abstract may be slightly abridged compared to the actual manuscript due to length limitations on arXi