A simulation-calibrated limit on the H i power spectrum from the GMRT Epoch of Reionization experiment

The Giant Metrewave Radio Telescope Epoch of Reionization experiment is an ongoing effort to measure the power spectrum from neutral hydrogen at high redshift. We have previously reported an upper limit of (70 mK)^2 at wavenumbers of k ≈ 0.65 h Mpc^(−1) using a basic piecewise-linear foreground subtraction. In this paper, we explore the use of a singular value decomposition to remove foregrounds with fewer assumptions about the foreground structure. Using this method, we also quantify, for the first time, the signal loss due to the foreground filter and present new power spectra adjusted for this loss, providing a revised measurement of a 2σ upper limit at (248 mK)^2 for k = 0.50 h Mpc^(−1). While this revised limit is larger than previously reported, we believe it to be more robust and still represents the best current constraint on reionization at z ≈ 8.6

Studying the History of the Intergalactic Medium with the SCI-HI Experiment

<p>The Cosmic Dawn (z ∼ 15 − 35) is the period in the history of our universe when stars first began to form in small Dark Matter minihalos. Light from these first stars is too dim for telescopes to see, which means that the Cosmic Dawn has never been directly measured. However, the first stars impacted the gas, or intergalactic medium (IGM), around them. The impact of the first stars was heating and eventual ionization of the IGM. The process of heating and ionization creates a spectrum that varies over redshift, namely the spatially averaged brightness temperature spectrum of 21-cm light from the IGM. Measurement of this spectrum will give us a first glimpse of the Cosmic Dawn. The ′′Sonda Cosmologica de las Islas para la Deteccion de Hidrogeno Neutro′′ (SCIHI) experiment is a collaboration between Carnegie Mellon University (CMU) and Instituto Nacional de Astrof´ısica, ´Optica y Electr´onica (INAOE) in Mexico and was designed to make this measurement. The SCI-HI experiment is a small-scale system which travels with the team to remote locations for deployments. These remote locations are necessary to avoid radio frequency interference and other environmental impacts on the system. This thesis describes the development and deployment of the SCI-HI experiment. It starts with the original design and covers development of the system over time. Deployment location selection is then discussed, including the results of site evaluations. In addition, the thesis outlines the data analysis process used for the system and shows results from data collected during the June 2013 deployment of the experiment. Finally, the thesis describes plans for the future of the SCI-HI experiment, including deployment to South Africa in 2015.</p

Probing the Dark Ages at Z~20: The SCI-HI 21 cm All-Sky Spectrum Experiment

<p>We present first results from the SCI-HI experiment, which we used to measure the all-sky-averaged 21 cm brightness temperature in the redshift range 14.8 < <em>z</em> < 22.7. The instrument consists of a single broadband sub-wavelength size antenna and a sampling system for real-time data processing and recording. Preliminary observations were completed in 2013 June at Isla Guadalupe, a Mexican biosphere reserve located in the Pacific Ocean. The data was cleaned to excise channels contaminated by radio frequency interference, and the system response was calibrated by comparing the measured brightness temperature to the Global Sky Model of the Galaxy and by independent measurement of Johnson noise from a calibration terminator. We present our results, discuss the cosmological implications, and describe plans for future work.</p