Paving the way to the detection of the global EoR with BIGHORNS
11 June 2015
The Epoch of Reionisation (EoR) is the time in the early Universe when the first stars and galaxies formed and re-ionised the neutral hydrogen. Indirect information about the EoR has been obtained from the Cosmic Microwave Background and spectra of distant quasars. However, the pinnacle of information about the physical parameters of the EoR is encoded in the 21cm line (1420 MHz) from neutral hydrogen that got redshifted into the low radio frequency range 200 – 50 MHz, for redshifts of 6 < z < 30. Multiple on-going projects ranging from interferometer arrays to single antenna experiments try to identify the elusive faint signal (in the order of milliKelvins) among the bright foregrounds (order of hundreds of Kelvins) and instrumental effects.
A team of CAASTRO researchers at Curtin University, led by Dr Marcin Sokolowski and Dr Randall Wayth, developed a portable, single antenna system called BIGHORNS – Broadband Instrument for Global Hydrogen Reionisation Signal – in order to detect the signature of the EoR in the sky-averaged radio spectrum, the so-called global EoR. For testing, the instrument was deployed in several remote and radio-quiet locations of Western Australia, and low radio frequency interference data were collected. The sky data in conjunction with many hours of laboratory test data allowed the team to develop a data analysis pipeline, to establish calibration procedures and to identify multiple instrumental effects which all resulted in further improvements to the system. Calibration of the signal from a single antenna down to milliKelvin precision as required for the detection of the global EoR is an extremely challenging task. However, the BIGHORNS team – equipped with valuable expertise and experience, as well as their new conical log spiral antenna, deployed at the CSIRO Murchison Radio-astronomy Observatory – is now hoping to push the boundaries and to get closer to detecting the global EoR signature.