CHIPS: The Cosmological HI Power Spectrum Estimator
15 February 2016
Exploring the neutral hydrogen from the first billion years of the Universe provides a wealth of information about the ionisation state, spatial structure and temperature of the intergalactic medium and the growth of the first stars, galaxies and black holes in the Universe. Neutral hydrogen is probed through its radio frequency emission line, observable from the early Universe with low-frequency radio telescopes. We are using the Murchison Widefield Array (MWA) to detect 12 billion year-old hydrogen, in an attempt to provide a first glimpse into the evolution of the Universe at this early time — the Epoch of Reionisation (EoR).
As part of the MWA EoR project, CAASTRO Associate Investigator Dr Cathryn Trott (Curtin University) and colleagues have designed, built and launched a sophisticated data analysis tool to take the complex data from the telescope and extract the tiny signal from the early Universe. The CHIPS Estimator (the "Cosmological HI Power Spectrum Estimator") is based on signal detection theory and a sound knowledge of the characteristics of our telescope, to seek an optimised measurement of the EoR signal. As one of the two primary signal estimation pipelines for the MWA, it uses data calibrated through the MWA Real Time System (RTS), developed by CAASTRO members at the University of Melbourne CAASTRO node, to extract the signal from the contaminated and noisy data.
In their recently-published paper in the Astrophysical Journal, the researchers define the mathematical framework for the CHIPS Estimator and then apply it to three hours of test data from the MWA EoR experiment. As a small subset of the >1000 hours of the full experiment, this "golden set" of data is being used by multiple groups to test and refine their analysis methods. The CHIPS Estimator was demonstrated to produce the expected signals from this dataset and provides an upper limit on the strength of the early Universe signal.