How well can we measure and understand foregrounds with 21-cm experiments?
Article first published online: 18 NOV 2011
© 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS
Monthly Notices of the Royal Astronomical Society
Volume 419, Issue 4, pages 3491–3504, February 2012
How to Cite
Liu, A. and Tegmark, M. (2012), How well can we measure and understand foregrounds with 21-cm experiments?. Monthly Notices of the Royal Astronomical Society, 419: 3491–3504. doi: 10.1111/j.1365-2966.2011.19989.x
- Issue published online: 9 JAN 2012
- Article first published online: 18 NOV 2011
- Accepted 2011 October 11. Received 2011 October 11; in original form 2011 June 10
- methods: data analysis;
- techniques: interferometric;
- dark ages, reionization, first stars;
- radio lines: general
Before it becomes a sensitive probe of the epoch of reionization, the dark ages and fundamental physics, 21-cm tomography must successfully contend with the issue of foreground contamination. Broad-band foreground sources are expected to be roughly 4 orders of magnitude larger than any cosmological signals, so precise foreground models will be necessary. Such foreground models often contain a large number of parameters, reflecting the complicated physics that governs foreground sources. In this paper, we concentrate on spectral modelling (neglecting, for instance, bright point source removal from spatial maps) and show that 21-cm tomography experiments will likely not be able to measure these parameters without large degeneracies, simply because the foreground spectra are so featureless and generic. However, we show that this is also an advantage, because it means that the foregrounds can be characterized to a high degree of accuracy once a small number of parameters (likely three or four, depending on one’s instrumental specifications) are measured. This provides a simple understanding for why 21-cm foreground subtraction schemes are able to remove most of the contaminants by suppressing just a small handful of simple spectral forms. In addition, this suggests that the foreground modelling process should be relatively simple and will likely not be an impediment to the foreground subtraction schemes that are necessary for a successful 21-cm tomography experiment.