1508.06503
The foreground wedge and 21 cm BAO surveys
Seo, Hirata
Redshifted H 21cm emission from unresolved low-z LSS is a promising window for ground-based BAO observations. One of the major challenges for this method is separating the cosmic signal that contains the BAO from the FGs of Galactic and extra-Galactic origins that are stronger by many orders of magnitude than the former. The smooth frequency spectrum expected for the FGs would nominally contaminate only very small k_|| modes; however the chromatic response of the telescope antenna pattern at this wavelength to the FG introduces non-smooth structure, pervasively contaminating the cosmic signal over the physical scales of interest. Such contamination defines a wedged volume in Fourier space around the transverse modes that is inaccessible for the cosmic signal. In this paper, test the effect of this contaminated wedge on the future 21 cm BAO surveys using Fisher information matrix calculation. Include the signal improvement due to the BAO construction technique that has been used for galaxy surveys and test the effect of this wedge on the BAO reconstruction as a function of signal to noises and incorporate the results in the Fisher matrix calculation. Find that the wedge effect expected at z=1-2 is very detrimental to the angular diameter distances: the errors on angular diameter distances increased by 3-4.4x, while the errors on H(z) increased by a factor of 1.5-1.6. Meanwhile the BAO reconstruction is still valuable for constraining the Hubble parameter even in the near absence of the transverse information and even in this low signal to noise regime (i.e., S/N<1) of the 21 cm surveys: for H(z) precision, observed 10-40% improvement depending on redshift and the noise level.
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