Colloq Abstract - Nhan
March 31, 2023
11:00am Mountain
Bang Nhan (NRAO)
Low-frequency instrument design and calibration approaches for low signal-to-noise sky-averaged 21-cm cosmology measurement
Radio telescopes have improved drastically in both spectral and spatial resolutions since the early radio antenna developed by Karl Guthe Jansky at Bell Lab in 1932. They enable astronomers to study the chemical compositions and dynamics of distant galaxies within the intergalactic medium (IGM). As the current IGM theory suggests, the most promising probe to study the early Universe (about 100 million years after the Big Bang), a period before and during the birth of the first stars and galaxies, is to measure the magnitude change as a function of observed frequency for the 21-cm spin-flip transition from the primordial neutral hydrogen atoms. As the Universe expands and evolves, the redshifted 21-cm signal is a direct proxy for the IGM’s thermal and ionization evolution when observed on Earth below 200 MHz. Incomplete sky survey along with lack of accurate antenna beam pattern measurement at low frequency are the two primary challenges in extracting the extremely weak cosmological signal for all 21-cm experiments. Among these two challenges are a slew of instrumental and observational systematics (e.g., receiver gain and noise stability, ionospheric distortion, soil property effect on the antenna’s EM performance) which can easily corrupt the extremely weak cosmological 21-cm signal. In this talk, I will provide an overview on the instrument design and calibration approaches our team have developed for the sky-averaged (global) 21-cm signal measurement, specifically in antenna design, receiver calibration scheme, environment characterization, and observation strategies. Some are also applicable to other frequency regimes and science requirements.
