Other
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21930401h&link_type=abstract
American Astronomical Society, AAS Meeting #219, #304.01
Other
Scientific paper
The highly redshifted 21-cm line of hydrogen promises to be an excellent probe of the cosmic dawn (when the first stars ignited) and the epoch of reionization. Interferometric measurements of 21-cm fluctuations require large telescopes with many antennas. The sky-averaged, 'global' signal, however, may be accessible with single-dipole experiments, even during the cosmic dawn, which will not be probed with the current generation of interferometers. Moreover, the global signal provides complementary information to the fluctuations. Extracting the signal may be challenging, however: the very large foregrounds require accurate modelling, and place stringent demands on the quality of the instrumental calibration. The challenge at first appears similar to that faced by interferometric experiments, but in detail it is rather different and may well require novel approaches. A number of experiments are under way or are proposed to measure the global 21-cm signal, and it has become more urgent to address the problem of signal extraction. We present a Markov Chain Monte Carlo technique to extract the signal from data simulated for the Dark Ages Radio Explorer (DARE) which would measure the 21-cm signal at 40-120 MHz from lunar orbit. Our modelling includes the 21-cm signal, diffuse Galactic and extragalactic foregrounds, the Sun, radiation emitted by and reflected from the Moon, and a detailed parametrized description of the properties of the instrument. We demonstrate that the signal parameters can be recovered accurately from realistic, noisy spectra with an experiment of reasonable duration, exploiting the spectral smoothness of the foregrounds and the spatial uniformity of the signal. Our method demonstrates the feasibility of DARE and validates its observational strategy, but is general and could be applied to other global 21-cm experiments. Moreover it may shed light on how to improve the design of these experiments.
Bowman Judd
Burns Jason
Harker Geraint
Pritchard Jonathan
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