Modes of the Dark Ages 21cm field accessible to a lunar radio interferometer
arxiv(2024)
摘要
At redshifts beyond z ≳ 30, the 21cm line from neutral hydrogen is
expected to be essentially the only viable probe of the 3D matter distribution.
The lunar far-side is an extremely appealing site for future radio arrays that
target this signal, as it is protected from terrestrial radio frequency
interference, and has no ionosphere to attenuate and absorb radio emission at
low frequencies (tens of MHz and below). We forecast the sensitivity of
low-frequency lunar radio arrays to the bispectrum of the 21cm brightness
temperature field, which can in turn be used to probe primordial
non-Gaussianity generated by particular early universe models. We account for
the loss of particular regions of Fourier space due to instrumental limitations
and systematic effects, and predict the sensitivity of different representative
array designs to local-type non-Gaussianity in the bispectrum, parametrised by
f_ NL. Under the most optimistic assumption of sample variance-limited
observations, we find that σ(f_ NL) ≲ 0.01 could be achieved
for several broad redshift bins at z ≳ 30 if foregrounds can be removed
effectively. These values degrade to between σ(f_ NL) ∼ 0.03 and
0.7 for z=30 to z=170 respectively when a large foreground wedge region
is excluded.
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