How well can we measure and understand foregrounds with 21 cm experiments?

Details How well can we measure and understand foregrounds with 21 cm experiments? How well can we measure and understand foregrounds with 21 cm experiments?

2011-05-31

arxiv.org/abs/1106.0007v3

MNRAS 419: 3491-3504 (2012)

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

15 pages, 9 figures, 2 tables; Replaced with accepted MNRAS version (slight quantitative changes to plots and tables, no chang

Scientific paper

10.1111/j.1365-2966.2011.19989.x

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. Broadband foreground sources are expected to be roughly four 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 modeling (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 modeling 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.

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